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The North American Numbering Plan (NANP) is a
telephone numbering plan A telephone numbering plan is a type of numbering scheme used in telecommunication to assign telephone numbers to subscriber telephones or other telephony endpoints. Telephone numbers are the addresses of participants in a telephone network, re ...
for twenty-five regions in twenty countries, primarily in North America and the Caribbean. This group is historically known as World Zone 1 and has the international calling code ''1''. Some North American countries, most notably Mexico, do not participate in the NANP. The NANP was originally devised in the 1940s by the
American Telephone and Telegraph Company AT&T Inc. is an American multinational telecommunications holding company headquartered at Whitacre Tower in Downtown Dallas, Texas. It is the world's largest telecommunications company by revenue and the third largest provider of mobile te ...
(AT&T) for the Bell System and the independent telephone operators in North America. The goal was to unify the diverse local numbering plans that had been established in the preceding decades and prepare the continent for direct-dialing of calls by customers without the involvement of telephone operators. AT&T continued to administer the numbering plan until the breakup of the Bell System, when administration was delegated to the North American Numbering Plan Administrator (NANPA), a service that has been procured from the private sector by the
Federal Communications Commission The Federal Communications Commission (FCC) is an independent agency of the United States federal government that regulates communications by radio, television, wire, satellite, and cable across the United States. The FCC maintains jurisdicti ...
(FCC) in the United States. Each participating country forms a regulatory authority that has plenary control over local numbering resources. The FCC also serves as the U.S. regulator. Canadian numbering decisions are made by the Canadian Numbering Administration Consortium. The NANP divides the territories of its members into numbering plan areas (NPAs) which are encoded numerically with a three-digit telephone number prefix, commonly called the area code. Each telephone is assigned a seven-digit
telephone number A telephone number is a sequence of digits assigned to a landline telephone subscriber station connected to a telephone line or to a wireless electronic telephony device, such as a radio telephone or a mobile telephone, or to other devices f ...
unique only within its respective numbering plan area. The telephone number consists of a three-digit central office (sometimes called "exchange") code and a four-digit station number. The combination of an area code and the telephone number serves as a destination routing address in the public switched telephone network (PSTN). The North American Numbering Plan conforms with
International Telecommunication Union The International Telecommunication Union is a specialized agency of the United Nations responsible for many matters related to information and communication technologies. It was established on 17 May 1865 as the International Telegraph Unio ...
(ITU) Recommendation E.164, which establishes an international numbering framework.


History

From the Bell System's beginnings in 1876 and throughout the first part of the 20th century, telephone networks grew from essentially local or regional telephone systems. These systems expanded by growing their subscriber bases, as well as increasing their service areas by implementing additional local exchanges that were interconnected with
tie trunk A tie line, also known as a tie trunk, is a telecommunication circuit between two telephone exchanges or two extensions of a private telephone system. See also *Private branch exchange * Circuit ID *Leased line *Private line In telecommunication ...
s. It was the responsibility of each local administration to devise telephone numbering plans that accommodated the local requirements and growth. As a result, the North American telephone service industry developed into an unorganized system of many differing local numbering systems. The diversity impeded the efficient operation and interconnection of exchanges into a nationwide system for long-distance telephone communication. By the 1940s, the Bell System set out to unify the various numbering plans in existence to provide a unified, systematic approach to route telephone calls across the nation and provide efficient long-distance service that eventually did not require the involvement of switchboard operators. In October 1947, AT&T published a new nationwide numbering plan in coordination with the independent telephone operators. The plan divided most of North America into eighty-six numbering plan areas (NPAs). Each NPA was assigned a unique three-digit code, typically called ''NPA code'' or simply ''area code''. These codes were first used in Operator Toll Dialing by long-distance operators in establishing calls via trunks between toll offices. The goal of automatic service required additional technical advancements in the latest generation of toll-switching systems, completed by the early 1950s, and installation of new toll-switching systems in most numbering plan areas. The first customer-dialed direct call using an area code was made on November 10, 1951, from Englewood, New Jersey, to
Alameda, California Alameda ( ; ; Spanish for " tree-lined path") is a city in Alameda County, California, located in the East Bay region of the Bay Area. The city is primarily located on Alameda Island, but also spans Bay Farm Island and Coast Guard Island, as we ...
.
Direct distance dialing Direct distance dialing (DDD) is a telecommunication service feature in North America by which a caller may, without operator assistance, call any other user outside the local calling area. Direct dialing by subscribers typically requires extra d ...
(DDD) was subsequently introduced across the country. By the early 1960s, DDD had become commonplace in cities and most towns in the United States and Canada. By 1967, the number of assigned area codes had grown to 129.AT&T, ''Notes on Distance Dialing'' (1968). The status of the network of the 1960s was reflected in a new name used in technical documentation: ''North American Integrated Network''. By 1975, the numbering plan was referred to as the ''North American Numbering Plan'',AT&T, ''Notes on Distance Dialing'' (1975). leading to the well-known acronym ''NANP'', as other countries sought or considered joining in the standardization.


Foreign expansion

Although
Bermuda ) , anthem = "God Save the King" , song_type = National song , song = "Hail to Bermuda" , image_map = , map_caption = , image_map2 = , mapsize2 = , map_caption2 = , subdivision_type = Sovereign state , subdivision_name = , es ...
and the Caribbean islands had been assigned the area code 809 as early as 1958 by the administrators at AT&T, individual participating countries or territories had no autonomy over their numbering plan as they received centrally assigned central office prefixes that needed to be unique from those of other countries with the same area code. Regions in Mexico with high call volumes to and from the US were assigned functional area codes as early as 1963, for the purpose of call routing, but a nationwide system of participation in the NANP eventually failed. In the following decades, the NANP expanded to include all of the United States and its territories,
Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...
, Bermuda, and seventeen nations of the Caribbean. At the request of the British Colonial Office, the numbering plan was first expanded to Bermuda and the
British West Indies The British West Indies (BWI) were colonized British territories in the West Indies: Anguilla, the Cayman Islands, Turks and Caicos Islands, Montserrat, the British Virgin Islands, Antigua and Barbuda, The Bahamas, Barbados, Dominica, Grena ...
because of their historic telecommunications administration through Canada as parts of the
British Empire The British Empire was composed of the dominions, colonies, protectorates, mandates, and other territories ruled or administered by the United Kingdom and its predecessor states. It began with the overseas possessions and trading posts e ...
and their continued associations with Canada, especially during the years of the telegraph and the
All Red Line The All Red Line was a system of electrical telegraphs that linked much of the British Empire. It was inaugurated on 31 October 1902. The informal name derives from the common practice of colouring the territory of the British Empire red or ...
system. Not all North American polities participate in the NANP. Exceptions include Mexico,
Greenland Greenland ( kl, Kalaallit Nunaat, ; da, Grønland, ) is an island country in North America that is part of the Kingdom of Denmark. It is located between the Arctic and Atlantic oceans, east of the Canadian Arctic Archipelago. Greenland i ...
,
Saint Pierre and Miquelon Saint Pierre and Miquelon (), officially the Territorial Collectivity of Saint-Pierre and Miquelon (french: link=no, Collectivité territoriale de Saint-Pierre et Miquelon ), is a self-governing territorial overseas collectivity of France in t ...
, the
Central America Central America ( es, América Central or ) is a subregion of the Americas. Its boundaries are defined as bordering the United States to the north, Colombia to the south, the Caribbean Sea to the east, and the Pacific Ocean to the west. ...
n countries and some Caribbean countries (
Cuba Cuba ( , ), officially the Republic of Cuba ( es, República de Cuba, links=no ), is an island country comprising the island of Cuba, as well as Isla de la Juventud and several minor archipelagos. Cuba is located where the northern Caribbea ...
, Haiti, the
French Caribbean The French West Indies or French Antilles (french: Antilles françaises, ; gcf, label=Antillean Creole, Antiy fwansez) are the parts of France located in the Antilles islands of the Caribbean: * The two overseas departments of: ** Guadeloupe, ...
and the
Dutch Caribbean The Dutch Caribbean (historically known as the Dutch West Indies) are the territories, colonies, and countries, former and current, of the Dutch Empire and the Kingdom of the Netherlands in the Caribbean Sea. They are in the north and south-wes ...
, except for
Sint Maarten Sint Maarten () is a constituent country of the Kingdom of the Netherlands in the Caribbean. With a population of 41,486 as of January 2019 on an area of , it encompasses the southern 44% of the divided island of Saint Martin, while the nort ...
). The only Spanish-speaking state in the system is the
Dominican Republic The Dominican Republic ( ; es, República Dominicana, ) is a country located on the island of Hispaniola in the Greater Antilles archipelago of the Caribbean region. It occupies the eastern five-eighths of the island, which it shares with ...
. Mexican participation was planned,AT&T, ''Notes on the Network'', Section 3, p.8 (1980) but implementation stopped after three area codes (706, 903 and 905) had been assigned, and Mexico opted for an international numbering format, using country code 52. The area codes in use were subsequently withdrawn in 1991. The Dutch Caribbean territory of Sint Maarten joined the NANP in September 2011, receiving
area code 721 Area code 721 is the telephone area code in the North American Numbering Plan (NANP) for Sint Maarten, a constituent country of the Kingdom of the Netherlands in the Caribbean. The area code was assigned in 2011 after membership of the country in t ...
. Sint Maarten shares the island with the French
Collectivity of Saint Martin The Collectivity of Saint Martin (french: Collectivité de Saint-Martin), commonly known as simply Saint Martin (, ), is an overseas collectivity of France in the West Indies in the Caribbean, on – but not identical with – the island of S ...
which, like the rest of the French Caribbean, is not part of the NANP.


Administration

The NANP is administered by the ''North American Numbering Plan Administrator'' (NANPA, formerly ''Administration''). This function is overseen by the Federal Communications Commission, which assumed the responsibility upon the breakup of the Bell System. The FCC solicits private sector contracts for the role of the administrator. Before the breakup of the Bell System, administration of the North American Numbering Plan was performed by AT&T's Central Services Organization. In 1984, this function was transferred to Bell Communications Research (''Bellcore''), a company created by the divestiture mandate to perform services for the newly created local exchange carriers. On January 19, 1998, the NANPA function was transferred to the IMS division of Lockheed Martin in Washington, D.C. In 1999, the contract was awarded to Neustar, a company spun off from Lockheed for this purpose. The contract was renewed in 2004, and again in 2012. On January 1, 2019, Somos assumed the NANPA function under a one-year bridge contract granted by the FCC with the goal of consolidating the NANPA function with the Pooling Administrator and identifying a long-term contract holder. On December 1, 2020, Somos secured the $76 million contract for a term of eight years against one other bidder.


Numbering plan

The vision and goal of the architects of the North American Numbering Plan was a system by which telephone subscribers in the United States and Canada could themselves dial and establish a
telephone call A telephone call is a connection over a telephone network between the called party and the calling party. First telephone call The first telephone call was made on March 10, 1876, by Alexander Graham Bell. Bell demonstrated his ability to "ta ...
to any other subscriber without the assistance of switchboard operators. While this required an expansion of most existing local numbering plans, many of which required only four or five digits to be dialed, or even fewer in small communities, the plan was designed to enable local telephone companies to make as few changes as possible in their systems.


Numbering plan areas and central offices

The new numbering plan divided the North American continent into regional service areas, called ''numbering plan areas'' (''NPA''s), primarily following the jurisdictional boundaries of U.S. states and Canadian provinces. Some states or provinces needed to be divided into multiple areas. NPAs were created in accordance with principles deemed to maximize customer understanding and minimize dialing effort while reducing plant cost.'' Notes on the Network'', AT&T (1980) Each NPA was identified by a unique three-digit code number that was prefixed to the local telephone number, when calling from one NPA to another. Within the same numbering plan area, dialing the area code was not necessary. The telephone exchanges–in the Bell System they were officially called ''central offices''–became local exchange points in the nationwide system. Each of them was also assigned a three-digit number unique within its NPA. The combination of NPA code and central office code served as a destination routing code for use by operators to reach any central office through the switching network.AT&T (1955) ''Notes on Nationwide Dialing'' Due to the numerical structure of the numbering system, each NPA was technically limited to 540 central offices. Although the limitation to 540 central offices required the most populous states to be divided into multiple NPAs, it was not the sole reason to subdivide a state. An important aspect was the existing infrastructure for call routing, which had developed in preceding decades independently of state boundaries. The rules of determining areas also attempted to avoid cutting across busy toll traffic routes, so that most toll traffic remained within an NPA, and outgoing traffic in one area would not be tributary to toll offices in an adjacent area.W.H. Nunn, ''Nationwide Numbering Plan'', Bell System Technical Journal 31(5), 851 (1952) As a result, New York state was initially divided into five areas, the most of any state.
Illinois Illinois ( ) is a state in the Midwestern United States. Its largest metropolitan areas include the Chicago metropolitan area, and the Metro East section, of Greater St. Louis. Other smaller metropolitan areas include, Peoria and Rockf ...
,
Ohio Ohio () is a state in the Midwestern region of the United States. Of the fifty U.S. states, it is the 34th-largest by area, and with a population of nearly 11.8 million, is the seventh-most populous and tenth-most densely populated. The sta ...
,
Pennsylvania Pennsylvania (; ( Pennsylvania Dutch: )), officially the Commonwealth of Pennsylvania, is a state spanning the Mid-Atlantic, Northeastern, Appalachian, and Great Lakes regions of the United States. It borders Delaware to its southeast, ...
, and
Texas Texas (, ; Spanish: ''Texas'', ''Tejas'') is a state in the South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2020, it is the second-largest U.S. state by ...
were assigned four NPAs each, and
California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the m ...
,
Iowa Iowa () is a state in the Midwestern region of the United States, bordered by the Mississippi River to the east and the Missouri River and Big Sioux River to the west. It is bordered by six states: Wisconsin to the northeast, Illinois to th ...
, and
Michigan Michigan () is a U.S. state, state in the Great Lakes region, Great Lakes region of the Upper Midwest, upper Midwestern United States. With a population of nearly 10.12 million and an area of nearly , Michigan is the List of U.S. states and ...
received three. Eight states and provinces were split into two NPAs. Traditionally, central office switching systems were designed to serve up to ten thousand subscriber numbers. Thus, subscribers were assigned four-digit line or station numbers. This rounded out the total number of digits in a subscriber telephone number to ten: a three-digit area code, three-digit central office code, and four digits for each line. This fixed format defined the North American Numbering Plan as a ''closed numbering plan'',AT&T, ''Notes on the Network'', Section 10, p.3 (1980). as opposed to developments in some other countries where the number of digits was not fixed. The closed numbering plan did not require the subscriber to dial all digits. When making a local call or a call within their numbering plan area, the area code was omitted, resulting in
seven-digit dialing Seven-digit dialing is a telephone dialing procedure customary in some territories of the North American Numbering Plan (NANP) for dialing telephone numbers in the same numbering plan area (NPA). NANP telephone numbers consist of ten digits, of wh ...
.
Ten-digit dialing Ten-digit dialing is a telephone dialing procedure in the countries and territories that are members of the North American Numbering Plan (NANP). It is the practice of including the area code of a telephone number when dialing to initiate a telep ...
was only necessary when placing ''foreign area'' calls to subscribers in another state or numbering plan area. Exceptions existed for communities located on NPA boundaries, so that uniform local dialing was still possible in historically established communities.


Initial numbering system

In 1947, AT&T completed the new design for a nationwide toll network that established the
original North American area codes The original North American area codes were established by the American Telephone & Telegraph Company (AT&T) in 1947, following the demonstration of regional Operator Toll Dialing during the World War II period. The program had the goal of speedin ...
. The new organization provided for 152 area codes, each with a capacity to serve up to 540 central offices.Ralph Mabbs, ''Nation-Wide Operator Toll Dialing—the Coming Way'', Bell Telephone Magazine 1947 p.180 Originally, only eighty-six area codes were assigned.
New Jersey New Jersey is a state in the Mid-Atlantic and Northeastern regions of the United States. It is bordered on the north and east by the state of New York; on the east, southeast, and south by the Atlantic Ocean; on the west by the Delaware ...
received the first NPA code in the new system,
area code 201 Area codes 201 and 551 are telephone area codes in the North American Numbering Plan in the U.S. State of New Jersey. Area code 201 was the area code assigned to the entire state of New Jersey in 1947, when the North American area code system ...
. The second area code,
202 Year 202 ( CCII) was a common year starting on Friday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Year of the Consulship of Severus and Antoninus (or, less frequently, year 955 '' Ab urbe condi ...
, was assigned to the
District of Columbia ) , image_skyline = , image_caption = Clockwise from top left: the Washington Monument and Lincoln Memorial on the National Mall, United States Capitol, Logan Circle, Jefferson Memorial, White House, Adams Morgan, ...
. The allocation of area codes was readjusted as early as 1948 to account for inadequacies in some metropolitan areas. For example, the
Indiana Indiana () is a U.S. state in the Midwestern United States. It is the 38th-largest by area and the 17th-most populous of the 50 States. Its capital and largest city is Indianapolis. Indiana was admitted to the United States as the 19th s ...
numbering plan area
317 Year 317 ( CCCXVII) was a common year starting on Tuesday (link will display the full calendar) of the Julian calendar. At the time, it was known as the Year of the Consulship of Gallicanus and Bassus (or, less frequently, year 1070 ''Ab urbe c ...
was divided to provide a larger numbering pool in the Indiana suburbs of
Chicago (''City in a Garden''); I Will , image_map = , map_caption = Interactive Map of Chicago , coordinates = , coordinates_footnotes = , subdivision_type = Country , subdivision_name ...
(
area code 219 Area code 219 is a telephone area code in the North American Numbering Plan for Northwest Indiana, including the state's portion of the Chicago metropolitan area, which includes Lake, Porter, La Porte, Newton, and Jasper Counties. The area cod ...
). Initially, states divided into multiple numbering plan areas were assigned area codes with the digit ''1'' in the second position, while areas that comprised entire states or provinces received codes with ''0'' as the middle digit. This rule was broken by the early 1950s, as NPAs with digit ''0'' in the middle had to be split, but until 1995 all area codes assigned had none other than the digits ''0'' and ''1'' in this position. The eight codes of the form ''N11'' (''N = 2–9'') were reserved as service codes. The easily recognizable codes of the form ''N00'' were available in the numbering plan, but were not initially included in assignments. Additional area code patterns were later assigned for other services; for example, the area codes ''N10'' were implemented for the Teletypewriter Exchange Service (TWX).


Central office codes

It was already common practice for decades that the digits ''0'' and ''1'' could not appear in the first two digits of the central office codes, because the system of using the first two letters of familiar names for central offices did not assign letters to these digits. The digit ''0'' was used for operator assistance, and ''1'', which is essentially a single pulse of loop interruption, was automatically ignored by most switching equipment of the time. Therefore, the 0/1 rule for the area code provided a convenient means to distinguish seven-digit dialing from ten-digit dialing. The use of
telephone exchange names A telephone exchange name or central office name was a distinguishing and memorable name assigned to a central office. It identified the switching system to which a telephone was connected, and facilitated the connection of telephone calls betwee ...
as part of telephone numbers had been a well-established practice, and this was preserved for convenience and expediency in the new network design. The letter-to-digit translations were printed on the face of every rotary dial in the metropolitan areas, according to a scheme designed by W.G. Blauvelt in 1917, that had been used in the Bell System in large metropolitan areas since the early 1920s. The network reorganization standardized this system to using a two-letter, five-digit (''2L-5N'') representation of telephone numbers in most exchanges in North America, or to using an equivalent all-numeric seven-digit numbering plans, as was practiced by some telephone companies.


All-number calling

All-number calling was a telephone numbering plan introduced in 1958, that converted telephone numbers with exchange names to a numeric representation of seven digits. The original plan of 1947 had been projected to be usable beyond the year 2000. However, by the late 1950s it became apparent that it would be outgrown by about 1975.AT&T, ''All-Number Calling Being Introduced In Bell System'', Bell Laboratories Record 38(12) p.470 (December 1960) The limitations for the usable leading digits of central office codes, imposed by using common names for central office names, and their leading two characters as guides for customer dialing could no longer be maintained when opening new central offices. By 1962 it was forecast that in 1985 the number of telephones in the nation would equal its population of 280 million and increase to 600 million telephones for 340 million people in 2000.Blair N.D., Cosgrove M.P. (AT&T), ''why all numbers?'', Bell Telephone Magazine, Autumn 1962, p.10 As a result, the North American telephone administrations first introduced letter combinations that could not be linked to a familiar pronounceable central office name. Finally, they sought the elimination of central office names and letter codes, and introduced ''all-number calling'' (ANC). Under all-number calling, the number of permissible central office prefixes increased from 540 to potentially 800, but the first two digits of the central office code were still restricted to the range ''2'' to ''9'', and the eight combinations that ended in ''11'' were reserved as special calling codes. This increased the numbering pool for central office codes to 640, and resulted in the partitioning of the prefix space (''000''—''999'') according to the table at the right.


Interchangeable central office codes

As the numbering plan grew in the 1960s under all-number calling, plan administrators at AT&T identified that by c. 1973 some of the largest area codes in urban centers might run out of central office prefixes to install more individual access lines. For relief in these cases, they finally removed the requirement that the middle digit of the central office code could not be ''0'' or ''1''. This resulted in the format of
interchangeable central office code In the North American Numbering Plan (NANP), interchangeable NPA and central office codes constituted a change in numbering plan design and policy, to mitigate exhaustion of the numbering resources of the ten-digit telephone numbers used in the clo ...
s, ''N X X'', where N=2–9, and X is any digit. The first cities that required this action, in 1974, were the cities of Los Angeles with area code 213 and New York with 212. This change also required modification of the local dialing procedures to distinguish local calls from long-distance calls with area codes. Requiring ''1'' to be dialed before the full number in some areas provided for area codes of the form ''N10'', such as 210 in the
San Antonio ("Cradle of Freedom") , image_map = , mapsize = 220px , map_caption = Interactive map of San Antonio , subdivision_type = Country , subdivision_name = United States , subdivision_type1= State , subdivision_name1 = Texas , subdivision_t ...
, Texas, area and 410 in eastern
Maryland Maryland ( ) is a state in the Mid-Atlantic region of the United States. It shares borders with Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; and Delaware and the Atlantic Ocean to ...
. Therefore, someone calling from
San Jose, California San Jose, officially San José (; ; ), is a major city in the U.S. state of California that is the cultural, financial, and political center of Silicon Valley and largest city in Northern California by both population and area. With a 2020 popu ...
, to
Los Angeles Los Angeles ( ; es, Los Ángeles, link=no , ), often referred to by its initials L.A., is the List of municipalities in California, largest city in the U.S. state, state of California and the List of United States cities by population, sec ...
before the change would have dialed 213-555-0123 and after the change 1-213-555-0123, which permitted the use of 213 as an exchange prefix in the San Jose area. The preceding ''1'' also ideally indicates a toll call; however, this is inconsistent across the NANP because the FCC has left it to the
U.S. state In the United States, a state is a constituent political entity, of which there are 50. Bound together in a political union, each state holds governmental jurisdiction over a separate and defined geographic territory where it shares its sove ...
public utilities commissions to regulate for traditional
landline A landline (land line, land-line, main line, home phone, fixed-line, and wireline) is a telephone connection that uses metal wires or optical fiber telephone line for transmission, as distinguished from a mobile cellular network, which uses ...
s, and it has since become
moot Moot may refer to: * Mootness, in American law: a point where further proceedings have lost practical significance; whereas in British law: the issue remains debatable * Moot court, an activity in many law schools where participants take part in s ...
for
mobile phone A mobile phone, cellular phone, cell phone, cellphone, handphone, hand phone or pocket phone, sometimes shortened to simply mobile, cell, or just phone, is a portable telephone that can make and receive calls over a radio frequency link whi ...
s and digital
VoIP Voice over Internet Protocol (VoIP), also called IP telephony, is a method and group of technologies for the delivery of voice communications and multimedia sessions over Internet Protocol (IP) networks, such as the Internet. The terms Internet t ...
services that now offer nationwide calling without the extra digit.


Interchangeable NPA codes

In 1995, the North American Numbering Plan Administrator removed the requirement that the middle digit of an area code had to be either ''0'' or ''1'', implementing fully interchangeable NPA and central office codes, that had already been anticipated since the 1960s, when interchangeable central office codes were sanctioned.


Modern plan

The NANP numbering format may be summarized in the ten-digit notation ''NXX NXX-XXXX'', where digits ''N'' denote any of ''2''–''9'', and ''X'' is any digit (''0''–''9''). Using 0 or 1 as the first digit of an area code or central office code is invalid, as is a 9 as the middle digit of an area code; these are trunk prefixes or reserved for North American Numbering Plan expansion. :For example, ''(234) 235-5678'' is a valid telephone number; with area code 234, central office prefix (exchange) 235, and line number 5678. The number ''(234) 911-5678'' is invalid, because the central office code must not be in the form N11. ''(314) 159-2653'' is invalid, because the office code must not begin with ''1''. ''(123) 234-5678'' is invalid, because the NPA must not begin with 0 or 1. Each three-digit area code has a capacity of 7,919,900 telephone numbers (7,918,900 in the United States). Despite the widespread use of fictional telephone numbers of the form ''NXX 555-XXXX'', only the block of line numbers from ''0100'' through ''0199'' are specifically reserved for this purpose, leaving the rest available for assignment. The country calling code for all countries participating in the NANP is ''1''. The prefix ''1'' is also used with the NANP for long-distance dialing.


Non-geographic services

The North American Numbering Plan recognizes the need for non-geographic services by designating certain numbering blocks for such purposes. Many of these telephone numbers are selected from the ''easily recognizable codes'' (ERCs). For system-wide toll-free calling, in which the receiving party is billed for the call, uses the number range with area codes of the form 8XX. Area code and central office prefixes for other non-geographic services have the form 5XX-NXX. As of January 2021, the codes 500, 521, 522, 533, 544, 566, 577, 588, 523, 524, 525, and 526 have been designated. These codes are used for fixed or mobile devices, and not assigned to rate centers. As addresses, they may or may not traverse the public switched telephone network (PSTN). Applications include the use as personal
500 500 may refer to: * 500 (number) * 500 BC * AD 500 Buildings and places * 500 Boylston Street of Boston * 500 Brickell in Miami * 500 Capitol Mall in Sacramento * 500 Fifth Avenue * 500 Renaissance Center, one of seven buildings in the GM Renaiss ...
numbers. Some carrier-specific services have used area code 700. In Canada, area code 600 is used for non-geographic applications. Area code 900 has been used for high-toll
900 number Premium-rate telephone numbers are telephone numbers that charge callers higher price rates for select services, including information and entertainment. A portion of the call fees is paid to the service provider, allowing premium calls to be an ...
s.


Cellular mobile services

The North American Numbering Plan does not set aside special non-geographic area codes exclusively for
cellular phones A mobile phone, cellular phone, cell phone, cellphone, handphone, hand phone or pocket phone, sometimes shortened to simply mobile, cell, or just phone, is a portable telephone that can make and receive calls over a radio frequency link while ...
, as is customary in some other national telephone administrations. Only one regional exception exists in area code 600 in Canada. For cellular services, telephone numbers in the NANP are allocated within each area code from special central office prefixes. Calls to them are billed at the same rate as any other call. Consequently, the ''caller pays'' pricing model adopted in other countries, in which calls to cellular phones are charged at a higher nationwide rate, but incoming mobile calls are not charged to the mobile user, could not be implemented. Instead, North American cellular telephone subscribers are also generally charged for receiving calls (''subscriber pays''). In the past, this has discouraged mobile users from publishing mobile telephone numbers, but by the first decade of the 21st century, most users selected bundle pricing plans that included an allotment of minutes expected to be used in the billing period, and most U.S. carriers now offer unlimited calling plans at mass-market prices. Industry observers have attributed the relatively low mobile phone penetration rate in the United States, compared to that of Europe, to the subscriber-pays model. In this model the convenience of the mobility is charged to the subscriber. Callers from outside the local-calling region of the assigned number, however, pay for a long-distance call, although domestic long-distance rates are generally lower than the rates in caller-pays systems. Conversely, an advantage of caller-pays is the relative absence of
telemarketing Telemarketing (sometimes known as inside sales, or telesales in the UK and Ireland) is a method of direct marketing in which a salesperson solicits prospective customers to buy products or services, either over the phone or through a subsequen ...
and nuisance calls to mobile numbers. The integrated numbering plan also enables
local number portability Local number portability (LNP) for fixed lines, and full mobile number portability (FMNP) for mobile phone lines, refers to the ability of a "customer of record" of an existing fixed-line or mobile telephone number assigned by a local exchange ca ...
between fixed and wireless services within a region, allowing users to switch to mobile service while keeping their telephone number. The initial plan for area code overlays did allow for providing separate area codes for use by mobile devices, although these were still assigned to a specific geographical area, and were charged at the same rate as other area codes. Initially, the area code 917 for
New York City New York, often called New York City or NYC, is the most populous city in the United States. With a 2020 population of 8,804,190 distributed over , New York City is also the most densely populated major city in the Un ...
was specifically assigned for this purpose within the boroughs; however, a Federal court overturned the practice and the use of an area code for a specific telephony purpose. Since mobile telephony has been expanding faster than landline use, new area codes typically have a disproportionately large fraction of mobile and nomadic numbers, although landline and other services rapidly follow and local network portability can blur these distinctions.


Growth

Canada and the United States have experienced rapid growth in the number of area codes, particularly between 1990 and 2005. The widespread adoption of
fax Fax (short for facsimile), sometimes called telecopying or telefax (the latter short for telefacsimile), is the telephonic transmission of scanned printed material (both text and images), normally to a telephone number connected to a printer o ...
,
modem A modulator-demodulator or modem is a computer hardware device that converts data from a digital format into a format suitable for an analog transmission medium such as telephone or radio. A modem transmits data by Modulation#Digital modulati ...
, and mobile phone communication, as well as the deregulation of local telecommunication services in the United States in the mid-1990s, increased the demand for telephone numbers. The Federal Communications Commission allowed telecommunication companies to compete with the incumbent local exchange carriers for services, usually by forcing the existing sole service provider to lease infrastructure to other local providers. Because of the original design of the numbering plan and the telephone switching network that assumed only a single provider, number allocations had to be made in 10,000-number blocks even when far fewer numbers were required for each new vendor. Due to the proliferation of service providers in some numbering plan areas, many area codes fell into ''jeopardy'', facing exhaustion of numbering resources. The number blocks of failed service providers often remained unused, as no regulatory mechanism existed to reclaim and reassign these numbers. Area codes are added by two principal methods, number plan area ''splits'' and '' overlays''. Splits were implemented by dividing an area into two or more regions, one of which retained the existing area code and the other areas receiving a new code. In an overlay, multiple codes are assigned to the same geographical area, obviating the need for renumbering of existing services. Subtle variations of these techniques have been used as well, such as ''dedicated overlays'', in which the new code is reserved for a particular type of service, such as cellular phones and pagers, and ''concentrated overlays'', in which a part of the area retained a single code while the rest of the region received an overlay code. The only service-specific overlay in the NANP was area code 917 (New York City) when it was first installed; such service-specific area code assignments were later prohibited by the Federal Communications Commission. Most area codes of the form N10, originally reserved for AT&T's
Teletypewriter eXchange The telex network is a station-to-station switched network of teleprinters similar to a telephone network, using telegraph-grade connecting circuits for two-way text-based messages. Telex was a major method of sending written messages electroni ...
(TWX) service, were transferred to Western Union in 1969 and were freed up for other use in 1981 after conversion to Telex II service was complete. The last of these, 610, was assigned to Canada, but reassigned in 1992. These new area codes, as well as a few other codes used for routing calls to Mexico, were used for telephone area code splits in the late 1980s and early 1990s, as all other area codes under the original plan had been consumed. After the remaining valid area codes were used up by expansion, in 1995 the rapid increase in the need for more area codes forced the NANPA to allow the digits 2 through 8 to be used as a middle digit in new area code assignments, with 9 being reserved as a ''last resort'' for potential future expansion. At the same time, local exchanges were allowed to use 1 or 0 as a middle digit. The first area codes without a 1 or 0 as the middle digit were
area code 334 Area code 334 is a telephone area code in the North American Numbering Plan (NANP) for southeastern Alabama. It was created on January 15, 1995, in an area code split from area code 205. and was the first new area code in Alabama since the impl ...
in Alabama and
area code 360 Area code 360 is the telephone area code for western Washington state outside metropolitan Seattle. It began service on January 15, 1995. The numbering plan area (NPA), which encompasses all of western Washington outside urban King, Pierce, and ...
in Washington, which both began service on January 15, 1995. This was quickly followed by
area code 520 Area code 520 is a telephone area code in the North American Numbering Plan (NANP) for the U.S. state of Arizona. The numbering plan area comprises Tucson and most of the southeastern part of the state. Area code 520 was created in a split from ...
serving Arizona on March 19, 1995. By 1995, many cities in the United States and Canada had more than one area code, either from dividing a city into different areas (NPA split) or having more than one code for the same area (NPA overlay). The overlay method requires that the area code must be dialed in all cases, even for local calls, while the split plan may permit seven-digit dialing within the same area. The transition to ten-digit dialing typically starts with a permissive dialing phase, which is widely publicized, during which dialing all ten digits is optional. After a period of several months, mandatory dialing begins, when seven-digit dialing is no longer permissible.
Atlanta Atlanta ( ) is the capital and most populous city of the U.S. state of Georgia. It is the seat of Fulton County, the most populous county in Georgia, but its territory falls in both Fulton and DeKalb counties. With a population of 498,715 ...
was the first U.S. city to require mandatory ten-digit dialing throughout the metropolitan area, roughly coinciding with the
1996 Summer Olympics The 1996 Summer Olympics (officially the Games of the XXVI Olympiad, also known as Atlanta 1996 and commonly referred to as the Centennial Olympic Games) were an international multi-sport event held from July 19 to August 4, 1996, in Atlanta, ...
held there. Atlanta was used as the test case not only because of its size, but also because it had the world's largest fiber-optic network at the time, five times larger than that of New York, and it was home to
BellSouth BellSouth, LLC (stylized as ''BELLSOUTH'' and formerly known as BellSouth Corporation) was an American telecommunications holding company based in Atlanta, Georgia. BellSouth was one of the seven original Regional Bell Operating Companies after ...
(now part of AT&T), then the Southeastern
Regional Bell Operating Company The Regional Bell Operating Companies (RBOC) are the result of '' United States v. AT&T'', the U.S. Department of Justice antitrust suit against the former American Telephone & Telegraph Company (later known as AT&T Corp.). On January 8, 1 ...
, with AT&T's fiber optics manufacturing facility within the city.


Growth issues

Depending on the techniques used for area code and central office code relief, the effect on telephone users varies. In areas in which overlays were used, this generally avoids the need for converting telephone numbers, so existing directories, business records, letterheads, business cards, advertising, and "speed-dialing" settings can retain the same phone numbers, while the overlay is used for new number allocations. The primary effect on telephone users is the necessity of remembering and dialing 10- or 11-digit numbers when only 7-digit dialing was previously permissible. Splitting instead of overlaying generally avoids the requirement for mandatory area-code dialing, but at the expense of having to convert a region to the new code. In addition to the requirements of updating records and directories to accommodate the new numbers, for efficient conversion this requires a period of "permissive dialing" in which the new and old codes are both allowed to work. Also, many splittings involved significant technical issues, especially when the area splittings occurred over boundaries other than phone network divisions. In 1998
area code 612 Metropolitan Minneapolis area codes with 612 in yellow Area code 612 is a telephone area code in the North American Numbering Plan (NANP) in the U.S. state of Minnesota. The numbering plan area comprises the city of Minneapolis and a few surr ...
, assigned to the
Minneapolis – Saint Paul Minneapolis () is the largest city in Minnesota, United States, and the county seat of Hennepin County. The city is abundant in water, with thirteen lakes, wetlands, the Mississippi River, creeks and waterfalls. Minneapolis has its origins ...
Twin Cities, was split to create
area code 651 Area code 651 is the telephone numbering plan code for Saint Paul, Minnesota, and the eastern suburbs of the Twin Cities. A dogleg portion also extends to the southeast along the Mississippi River to include cities such as Hastings. The region ...
for
St. Paul Paul; grc, Παῦλος, translit=Paulos; cop, ⲡⲁⲩⲗⲟⲥ; hbo, פאולוס השליח (previously called Saul of Tarsus;; ar, بولس الطرسوسي; grc, Σαῦλος Ταρσεύς, Saũlos Tarseús; tr, Tarsuslu Pavlus; ...
and the eastern metropolitan area. The
Minnesota Public Utilities Commission The Minnesota Public Utilities Commission (PUC) is the consumer protection agency in the U.S. state of Minnesota charged with the regulation of public utilities such as electric Electricity is the set of physical phenomena associated wi ...
mandated that the new boundary exactly follow municipal boundaries, which were distinctly different from telephone exchange boundaries, and that all subscribers keep their seven-digit numbers. These two goals were directly at odds with the reason for the split, namely to provide additional telephone numbers. More than forty exchanges had territory that straddled the new boundary. As a result, prefixes were duplicated in both area codes, which counteracted much of the benefit of the split, with only 200 of 700 prefixes in area 612 moving entirely to area 651. In less than two years area code 612 again exhausted its supply of telephone numbers, and required a three-way split in 2000, creating the new area codes
763 Year 763 ( DCCLXIII) was a common year starting on Saturday (link will display the full calendar) of the Julian calendar. The denomination 763 for this year has been used since the early medieval period, when the Anno Domini calendar era became ...
and
952 Year 952 ( CMLII) was a leap year starting on Thursday (link will display the full calendar) of the Julian calendar. Events By place Europe * Summer – At the Reichstag in Augsburg (assembled by King Otto I), joined by German nob ...
. The split followed political boundaries, rather than rate center boundaries, resulting in additional split prefixes; a few numbers moved from 612 to 651 and then to 763 in less than two years.


Decrease of growth rate

Recognizing that the proliferation of area codes was largely due to the telecom deregulation act and the assignment of numbers in blocks of ten thousand, the FCC instructed NANPA, by then administered by Neustar, to alleviate the numbering shortage. As a result,
number pooling Number pooling is a method of reallocating telephony numbering space in the North American Numbering Plan, primarily in growth areas in the United States. Instead of allocating blocks of ten thousand numbers to each carrier in each community, a bl ...
was piloted in 2001 as a system for allocating local numbers to carriers in blocks of 1,000 rather than 10,000. Because of the then design of the switched telephone network, this was a considerable technical obstacle. Number pooling was implemented with another technical obstacle,
local number portability Local number portability (LNP) for fixed lines, and full mobile number portability (FMNP) for mobile phone lines, refers to the ability of a "customer of record" of an existing fixed-line or mobile telephone number assigned by a local exchange ca ...
. The program has been implemented in much of the United States by state regulators. Some cities have also implemented rate center consolidation; fewer rate centers resulted in more efficient use of telephone numbers, as carriers would reserve blocks of 1,000 or 10,000 numbers in each of multiple rate centers in the same area even if they had relatively few clients in the area. (A rate center is a geographical area used by a Local Exchange Carrier (LEC) to determine the boundaries for local calling, billing and assigning phone numbers. Typically a call within a rate center is local, while a call from one rate center to another is a long-distance call.) Together with aggressive reclamation of unused number blocks from telecom providers, number pooling has reduced the need for additional area codes, so that many previously designated area splits and overlays have been postponed indefinitely. Canada never implemented number pooling, so that even the smallest villages are rate centers and every CLEC is assigned blocks of ten thousand numbers.


New area codes outside the contiguous United States and Canada

Before 1995, all NANP countries and territories outside the contiguous United States, Alaska, Hawaii and Canada shared the area code 809. This included
Puerto Rico Puerto Rico (; abbreviated PR; tnq, Boriken, ''Borinquen''), officially the Commonwealth of Puerto Rico ( es, link=yes, Estado Libre Asociado de Puerto Rico, lit=Free Associated State of Puerto Rico), is a Caribbean island and unincorporated ...
and the U.S. Virgin Islands. Each has since been assigned one or more distinct numbering plan areas; area code
809 __NOTOC__ Year 809 (Roman numerals, DCCCIX) was a common year starting on Monday (link will display the full calendar) of the Julian calendar. Events By place Byzantine Empire * Spring – Siege of Serdica (809), Siege of Serdica: ...
now exclusively serves the Dominican Republic (along with area codes 829 and 849). The United States Pacific territories of the
Northern Mariana Islands The Northern Mariana Islands, officially the Commonwealth of the Northern Mariana Islands (CNMI; ch, Sankattan Siha Na Islas Mariånas; cal, Commonwealth Téél Falúw kka Efáng llól Marianas), is an unincorporated territory and commonw ...
and
Guam Guam (; ch, Guåhan ) is an organized, unincorporated territory of the United States in the Micronesia subregion of the western Pacific Ocean. It is the westernmost point and territory of the United States (reckoned from the geographic cent ...
joined the NANP in 1997, and
American Samoa American Samoa ( sm, Amerika Sāmoa, ; also ' or ') is an unincorporated territory of the United States located in the South Pacific Ocean, southeast of the island country of Samoa. Its location is centered on . It is east of the Internationa ...
became an NANP member in October 2004. The Dutch possession of Sint Maarten was originally scheduled to join the NANP on May 31, 2010, but the changeover was postponed to September 30, 2011.


Telephone number size expansion

The NANP exhaust analysis estimates that the existing numbering system is sufficient beyond 2049, based on the assumptions that a maximum of 674 NPAs continue to be available, and that on average 3,990 central office codes are needed per year. In case of exhaustion, various plans are discussed for expanding the numbering plan. One option is to add the digit 1 or 0 either at the beginning or at the end of the area code, or prefixing it to the seven-digit subscriber number. This would require eleven-digit dialing even for local calls between any two NANP numbers. Another proposal introduces the digit ''9'' into the area code in the format ''x9xx'', so that, for example,
San Francisco San Francisco (; Spanish for " Saint Francis"), officially the City and County of San Francisco, is the commercial, financial, and cultural center of Northern California. The city proper is the fourth most populous in California and 17th ...
's ''415'' would become ''4915''. Other proposals include reallocating blocks of numbers assigned to smaller long-distance carriers or unused reserved services.


Dialing procedures

The structure of the North American Numbering Plan permits implementation of local
dial plan In telecommunication, a dial plan (or dialing plan) establishes the permitted sequences of digits dialed by telephone subscriber and the manner in which a telephone switch interprets these digits within the definitions of the prevailing telephone nu ...
s in each plan area, depending on requirements. When multiple NPA codes serve an area in an overlay arrangement, ten-digit (10D) dialing is required. Seven-digit (7D) dialing may be permissible in areas with single area codes. Depending on the requirement of toll alerting, it may be necessary to prefix a telephone number with ''1''. The NANPA publishes dial plan information for individual area codes. The standard dial plans in most cases are as follows: The number of digits dialed is unrelated to being a local call or a toll call when there is no toll alerting. Allowing 7D local dial across an area code boundary, which is uncommon today, requires central office code protection, locally if using toll alerting, across the entire area code otherwise, to avoid assignment of the same seven-digit number on both sides. Landlines occasionally require 1+10D where 10D is required, most notably in California. Most areas permit local calls as 1+10D except for Texas, Georgia, and some jurisdictions in Canada which require that landline callers know which numbers are local and which are toll, dialing 10D for local calls and 1+10D for all toll calls. In almost all cases, domestic operator-assisted calls are dialed 0+10D.


Special numbers and codes

Some common special numbers in the North American system: * 0 – Operator assistance * 00 – Long-distance operator assistance (formerly 2-1-1) *
011 The following is a list of different international call prefixes that need to be dialled when placing an international telephone call from different countries. Countries by international prefix Countries using optional carrier selection code ...
– International access code using direct dial (for all destinations outside the NANP). * 01 – International access code using operator assistance (for all destinations outside the NANP). * 101-xxxx – Used to select use of an alternative long-distance carrier *
211 Year 211 ( CCXI) was a common year starting on Tuesday of the Julian calendar. At the time, in the Roman Empire it was known as the Year of the Consulship of Terentius and Bassus (or, less frequently, year 964 ''Ab urbe condita''). The denomin ...
– Local community information or social services (in some cities) * 311 – City government or non-emergency police matters *
411 411 may refer to: * The year AD 411, the four hundred and eleventh year of the Gregorian calendar * 411 BC * 4-1-1, a telephone directory assistance number in the United States and Canada ** By extension, a slang term for "information" * ''What's t ...
– Local telephone directory service (Some telephone companies provide national directory assistance) * 511 – Traffic, road, and tourist information *
611 __NOTOC__ Year 611 (Roman numerals, DCXI) was a common year starting on Friday (link will display the full calendar) of the Julian calendar. The denomination 611 for this year has been used since the early medieval period, when the Anno Domini ...
– Telephone line repair service (formerly 4104), wireless operator customer service (formerly 811). * 711 – Relay service for customers with hearing or speech disabilities. *
811 __NOTOC__ Year 811 ( DCCCXI) was a common year starting on Wednesday (link will display the full calendar) of the Julian calendar. Events By place Byzantine Empire * Byzantine–Bulgarian War: Emperor Nikephoros I organises a new ca ...
– Local
utility location Utility location is the process of identifying and labeling public utility mains that are underground. These mains may include lines for telecommunication, electricity distribution, natural gas, cable television, fiber optics, traffic lights, str ...
services (United States), non-urgent
telehealth Telehealth is the distribution of health-related services and information via electronic information and telecommunication technologies. It allows long-distance patient and clinician contact, care, advice, reminders, education, intervention, mon ...
/teletriage services in Canada (formerly telephone company business office) * 911
Emergency telephone number Most public switched telephone networks have a single emergency telephone number (sometimes known as the universal emergency telephone number or the emergency services number) that allows a caller to contact local emergency services for assis ...
– fire department, medical emergency, police. * 988
National Suicide Prevention Lifeline The 988 Suicide & Crisis Lifeline (formerly known as the National Suicide Prevention Lifeline) is a United States-based suicide prevention network of over 200+ crisis centers that provides 24/7 service via a toll-free hotline with the number 9- ...
(United States). * 950-xxxx –
Feature group A feature group, in North American telephone industry jargon, is most commonly used to designate various standard means of access by callers to competitive long-distance services. They defined switching arrangements from local exchange carrier ...
code for access to a carrier from a non-subscriber location. The feature requires the customer dial a 950-xxxx number and enter a calling card number and destination telephone number. It was originally used for locations where 101-xxxx dialing was not possible. * 958-xxxx (local); 959-xxxx (long distance) –
Plant test number In telecommunications, a plant test number is a telephone number reserved for use by telephone installers or other workers to test an individual telephone line. Test number are typically unlisted. The North American Numbering Plan The North Am ...
s, such as
automatic number announcement circuit An automatic number announcement circuit (ANAC) is a component of a central office of a telephone company that provides a service to installation and service technicians to determine the telephone number of a telephone line. The facility has a tel ...
s. It was once common to reserve entire unused exchange prefixes or N11 numbers (4101 was
ringback number A ringback number is a telephone number for a telephone line that automatically calls the line that the call was placed from, after the caller has hung up. The typical use of this facility is by telephone company technicians for testing a new insta ...
on many step-by-step switches), but these have largely moved to individual unpublished numbers within the standard 958-xxxx (local) or 959-xxxx (long-distance) plant test exchanges as numbers become scarce. * 1 (NPA) 555-1212 – Non-local directory information (Canada and United States)
Vertical service code A vertical service code (VSC) is a sequence of digits and the signals star (*) and number sign (#) dialed on a telephone keypad or rotary dial to enable or disable certain telephone service features. Some vertical service codes require dialing of ...
s are used for special calling features, such as: * *51 and 1151: A history of unanswered calls on a telephone number, useful for those who are not
Caller ID Caller identification (Caller ID) is a telephone service, available in analog and digital telephone systems, including voice over IP (VoIP), that transmits a caller's telephone number to the called party's telephone equipment when the call i ...
subscribers. * *57 and 1157: Used to trace harassing, threatening, abusive, obscene, etc. phone calls, and keep results of trace at phone company. * *66 and 1166: To keep retrying a busy-line (see also Called-party camp-on) * *67 and 1167: Caller ID Block * *69 and 1169: Call Return ''caller may press '1' to return call after hearing number'' * *70 and 1170: Cancel call waiting on a call-by-call basis * *71 and 1171: Three-way calling, which lets a person talk to people in two different locations at the same time. * *74 and 1174: Speed dial, which allows someone to quickly dial any of eight frequently called numbers using a one-digit code, from any phone on their line. * *75 allows a total of 30 speed-call numbers with two digits. * *77 activates Anonymous Call Rejection Service * *82 and 1182: Releases Caller ID block on a call-by-call basis * *87 deactivates Anonymous Call Rejection Service The four-digit numbers are not implemented in some areas. The star codes (*) are for use on Touch-Tone
telephone A telephone is a telecommunications device that permits two or more users to conduct a conversation when they are too far apart to be easily heard directly. A telephone converts sound, typically and most efficiently the human voice, into e ...
s, whereas the four-digit numbers prefixed 11xx are used on rotary dial telephones which cannot dial the * symbol. Not all NANP countries use the same codes. For example, the emergency telephone number is not always 911:
Trinidad and Tobago Trinidad and Tobago (, ), officially the Republic of Trinidad and Tobago, is the southernmost island country in the Caribbean. Consisting of the main islands Trinidad and Tobago, and numerous much smaller islands, it is situated south of ...
and Dominica use
999 999 or triple nine most often refers to: * 999 (emergency telephone number), a telephone number for the emergency services in several countries * 999 (number), an integer * AD 999, a year * 999 BC, a year Books * ''999'' (anthology) or ''999: T ...
, as in the
United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the European mainland, continental mainland. It comprises England, Scotlan ...
. The country of
Barbados Barbados is an island country in the Lesser Antilles of the West Indies, in the Caribbean region of the Americas, and the most easterly of the Caribbean Islands. It occupies an area of and has a population of about 287,000 (2019 estimate) ...
uses 211 for
police The police are a constituted body of persons empowered by a state, with the aim to enforce the law, to ensure the safety, health and possessions of citizens, and to prevent crime and civil disorder. Their lawful powers include arrest and th ...
force, 311 for
fire Fire is the rapid oxidation of a material (the fuel) in the exothermic chemical process of combustion, releasing heat, light, and various reaction products. At a certain point in the combustion reaction, called the ignition point, flames a ...
, and 511 for
ambulance An ambulance is a medically equipped vehicle which transports patients to treatment facilities, such as hospitals. Typically, out-of-hospital medical care is provided to the patient during the transport. Ambulances are used to respond to medi ...
, while
Jamaica Jamaica (; ) is an island country situated in the Caribbean Sea. Spanning in area, it is the third-largest island of the Greater Antilles and the Caribbean (after Cuba and Hispaniola). Jamaica lies about south of Cuba, and west of His ...
uses 114 for directory assistance, 119 for police force, and 110 for
fire Fire is the rapid oxidation of a material (the fuel) in the exothermic chemical process of combustion, releasing heat, light, and various reaction products. At a certain point in the combustion reaction, called the ignition point, flames a ...
and
ambulance An ambulance is a medically equipped vehicle which transports patients to treatment facilities, such as hospitals. Typically, out-of-hospital medical care is provided to the patient during the transport. Ambulances are used to respond to medi ...
services. Despite its early importance as a share of the worldwide telephone system, few of the NANP's codes, such as 911, have been adopted outside the system. Determining that 911 requires unnecessary rotation time on rotary dial telephones, the
European Union The European Union (EU) is a supranational political and economic union of member states that are located primarily in Europe. The union has a total area of and an estimated total population of about 447million. The EU has often been de ...
has adopted its own standardized number of 112, while countries in Asia and the rest of the world use a variety of other two- or three-digit emergency telephone number combinations. The 112 code is gaining prevalence because of its preprogrammed presence in mobile telephones that conform to the European
GSM The Global System for Mobile Communications (GSM) is a standard developed by the European Telecommunications Standards Institute (ETSI) to describe the protocols for second-generation ( 2G) digital cellular networks used by mobile devices such ...
standard. The European Union and many other countries have chosen the
International Telecommunication Union The International Telecommunication Union is a specialized agency of the United Nations responsible for many matters related to information and communication technologies. It was established on 17 May 1865 as the International Telegraph Unio ...
's 00 as their international access number instead of 011. The toll-free prefix 800 has been widely adopted elsewhere, including as the international toll-free country code. It is often preceded by a 0 rather than a 1 in many countries where 0 is the
trunk prefix A trunk prefix is a digit sequence to be dialed before a telephone number to initiate a telephone call for the purpose of selecting an appropriate telecommunications circuit by which the call is to be routed. Making a domestic (national) telephone ...
.


International dialing

While international direct dialing was available in some locations in the United States by the late 1950s, a continental system was introduced as International Direct Distance Dialing (IDDD) for the territories of the North American Numbering Plan in March 1970. While the NANP was designed as a ''closed numbering plan'' with ten digit telephone numbers, IDDD was implemented through extensive modifications in the switching systems to accommodate the international ''open numbering plan'' with seven to twelve digits in the national telephone numbers. Access to the international network is facilitated by the dialing prefix ''011'', after which the country calling code and the national telephone number are dialed.


Number portability

The
Telecommunications Act of 1996 The Telecommunications Act of 1996 is a United States federal law enacted by the 104th United States Congress on January 3, 1996, and signed into law on February 8, 1996, by President Bill Clinton. It primarily amended Chapter 5 of Title 47 of ...
( (b)(2)) authorizes the Federal Communications Commission (FCC) to require all local exchange carriers (LECs) to offer
local number portability Local number portability (LNP) for fixed lines, and full mobile number portability (FMNP) for mobile phone lines, refers to the ability of a "customer of record" of an existing fixed-line or mobile telephone number assigned by a local exchange ca ...
. The FCC regulations were enacted on June 27, 1996, with changes to take effect in the one hundred largest
Metropolitan Statistical Area In the United States, a metropolitan statistical area (MSA) is a geographical region with a relatively high population density at its core and close economic ties throughout the area. Such regions are neither legally incorporated as a city or tow ...
s by October 1, 1997, and elsewhere by December 31, 1998. The FCC directed the
North American Numbering Council The North American Numbering Council is an advisory committee of the Federal Communications Commission (FCC) of the United States, chartered in 1995. Its function is to develop and recommend efficient and fair administrative procedures in the admini ...
(NANC) to select one or more private-sector candidates for the local number portability administrator (LNPA) function, in a manner akin to the selection of the North American Numbering Plan Administrator (NANPA). The
toll-free telephone number A toll-free telephone number or freephone number is a telephone number that is billed for all arriving calls. For the calling party, a call to a toll-free number from a landline is free of charge. A toll-free number is identified by a dialing pre ...
s in NPA 800, 888, 877, 866, 855, 844, and 833 have been portable through the
RespOrg In the North American Numbering Plan, a RespOrg (a contraction for responsible organization) is a company that maintains the registration for individual toll-free telephone numbers in the distributed Service Management System/800 database. Their fun ...
system since 1993.


Toll charges

Calls between different countries and territories of the NANP are not typically charged at domestic rates. For example, most long-distance plans may charge a California subscriber a higher rate for a call to British Columbia than for a call to New York, even though both destinations are within the NANP. Similarly, calls from Bermuda to U.S. numbers (including 1-800 numbers, which are normally thought of as
toll-free A toll-free telephone number or freephone number is a telephone number that is billed for all arriving calls. For the calling party, a call to a toll-free number from a landline is free of charge. A toll-free number is identified by a dialing pref ...
) incur international rates. This is because many of the island nations implemented a plan of subsidizing the cost of local phone services by directly charging higher pricing levies on international long-distance services. Because of these higher fees,
scam A confidence trick is an attempt to defraud a person or group after first gaining their trust. Confidence tricks exploit victims using their credulity, naïveté, compassion, vanity, confidence, irresponsibility, and greed. Researchers hav ...
s had taken advantage of customers' unfamiliarity with pricing structure to call the legacy regional area code 809. Some scams lured customers from the United States and Canada into placing expensive calls to the Caribbean, by representing area code
809 __NOTOC__ Year 809 (Roman numerals, DCCCIX) was a common year starting on Monday (link will display the full calendar) of the Julian calendar. Events By place Byzantine Empire * Spring – Siege of Serdica (809), Siege of Serdica: ...
as a regular domestic, low-cost, or toll-free call. The split of 809 (which formerly covered all of the Caribbean NANP points) into multiple new area codes created many new, unfamiliar prefixes which could be mistaken for U.S. or Canada domestic area codes but carried high tariffs. In various island nations, premium exchanges such as +1-876-HOT-, +1-876-WET- or +1-876-SEX- (where 876 is Jamaica) became a means to circumvent consumer-protection laws governing area code 900 or similar U.S.-domestic premium numbers. These scams are on the decline, with many of the Cable and Wireless service monopolies being opened up to competition, hence bringing rates down. Additionally, many Caribbean territories have implemented local government agencies to regulate telecommunications rates of providers.


Countries and territories

Of all states or territories, the U.S. state of California has the largest number of area codes assigned, followed by Texas, Florida and New York, while most countries of the Caribbean use only one. Many Caribbean codes were assigned based on alphabetic abbreviations of the territory name, as indicated in the third column of the following table (''Letter code''). This follows the traditional letter assignments on telephone dials. For some Pacific islands, the NANPA area code is the same as the
country code Country codes are short alphabetic or numeric geographical codes (geocodes) developed to represent countries and dependent areas, for use in data processing and communications. Several different systems have been developed to do this. The term ...
that was discontinued upon membership in the NANP. Membership in the NANP brings significant advantages for countries in the vicinity of the United States and Canada, which usually are already the top dialing destinations. Both countries also originate most of the tourism business for the Caribbean. This is enhanced by the integration from sharing the same dialing procedures, without international access codes, and the toll-free number system of the NANP, as businesses in all member countries are eligible to participate.


Alphabetic mnemonic system

Many telephone dials and keypads maintain a tradition of alphabetic dialing. Usually each pushbutton from digit 2 to 9 also displays three letters, which is standardized in ISO 9995-8 and, in Europe, E.161. Historically, the letters Q and Z were omitted, although some modern telephones contain them. SMS-capable devices have all 26 letters. The alphabet is apportioned to the buttons as follows: No letters are typically mapped to keys ''1'' and ''0'', although some corporate
voicemail A voicemail system (also known as voice message or voice bank) is a computer-based system that allows users and subscribers to exchange personal voice messages; to select and deliver voice information; and to process transactions relating to ind ...
systems use 1 for Q and Z, and some old telephones assigned the Z to the digit 0. Originally, this scheme was used as a mnemonic device for the exchange prefixes in telephone numbers. When telephone numbers in the United States were standardized in the mid-20th century to seven digits, the first two digits of the exchange prefix were expressed as letters rather than numbers, using the telephone exchange name. Before
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposing ...
, the largest cities used three letters and four or five numerals, while in most cities phone numbers had only six digits (2L-4N). The prefix was a name and the first two or three letters, listed as capital letters in directories, were dialed. Later, the third letter, where implemented, was replaced by a digit, or an extra digit was added. This generally happened after World War II, although New York City converted in 1930. The adoption of seven-digit local numbers (2L-5N) was chosen as the requirement for
direct distance dialing Direct distance dialing (DDD) is a telecommunication service feature in North America by which a caller may, without operator assistance, call any other user outside the local calling area. Direct dialing by subscribers typically requires extra d ...
and progressively deployed starting in the late 1940s. The famous Glenn Miller tune '' PEnnsylvania 6-5000'' refers to telephone number PE6-5000, a number in service at the
Hotel Pennsylvania The Hotel Pennsylvania was a historic hotel at 401 Seventh Avenue (15 Penn Plaza) in Manhattan, across the street from Pennsylvania Station and Madison Square Garden in New York City. Opened in 1919, it was once the largest hotel in the world. ...
(212 736–5000) in New York up until 2020 when the hotel closed permanently. Similarly, the classic film ''
BUtterfield 8 ''BUtterfield 8'' is a 1960 American drama film directed by Daniel Mann, starring Elizabeth Taylor and Laurence Harvey. Taylor won her first Academy Award for her performance in a leading role. The film was based on a 1935 novel of the same na ...
'' is set in the East Side of
Manhattan Manhattan (), known regionally as the City, is the most densely populated and geographically smallest of the five boroughs of New York City. The borough is also coextensive with New York County, one of the original counties of the U.S. state ...
between roughly 64th and 86th Streets, where the telephone prefixes include 288. The letter system was phased out, beginning before 1965, although it persisted ten years later in some places. It was included in
Bell of Pennsylvania Verizon Pennsylvania LLC, formerly traded as Bell of Pennsylvania, is the Bell Operating Company serving most of Pennsylvania. The company was founded in 1879 as Bell Telephone Company of Philadelphia, owned by National Bell Telephone Company, wh ...
directories until 1983. Even today, some businesses still display a 2L-5N number in advertisements, e.g., the Belvedere Construction Company in
Detroit Detroit ( , ; , ) is the largest city in the U.S. state of Michigan. It is also the largest U.S. city on the United States–Canada border, and the seat of government of Wayne County. The City of Detroit had a population of 639,111 at t ...
, Michigan not only still uses the 2L-5N format for its number (TYler 8-7100), it uses the format for the toll-free number (1-800-TY8-7100). Despite the phasing out of the letter system, alphabetic
phoneword Phonewords are mnemonic phrases represented as alphanumeric equivalents of a telephone number. In many countries, the digits on the telephone keypad also have letters assigned. By replacing the digits of a telephone number with the correspondin ...
s remain as a commercial
mnemonic A mnemonic ( ) device, or memory device, is any learning technique that aids information retention or retrieval (remembering) in the human memory for better understanding. Mnemonics make use of elaborative encoding, retrieval cues, and imag ...
gimmick, particularly for toll-free numbers. For example, one can dial 1-800-FLOWERS to order flowers, or 1-800-DENTIST to find a local dentist. In addition to commercial uses, alphabetic dialing has occasionally influenced the choice of area codes. For example, when
area code 423 Area code 423 is a telephone area code in the North American Numbering Plan for the U.S. state of Tennessee. It comprises two disconnected areas of East Tennessee that are separated by area code 865. Principal cities in the northern part of t ...
( East Tennessee) was split in 1999, the region surrounding
Knoxville Knoxville is a city in and the county seat of Knox County in the U.S. state of Tennessee. As of the 2020 United States census, Knoxville's population was 190,740, making it the largest city in the East Tennessee Grand Division and the state' ...
was assigned
area code 865 Area code 865 serves Knoxville, Tennessee, and the nine surrounding counties ( Anderson, Blount, Grainger, Jefferson, Knox, Loudon, Roane, Sevier, and Union) in central East Tennessee. The area incorporates most of the region defined as the ...
, chosen to represent ''VOL'', for ''The Volunteer State'', the nickname of
Tennessee Tennessee ( , ), officially the State of Tennessee, is a landlocked state in the Southeastern region of the United States. Tennessee is the 36th-largest by area and the 15th-most populous of the 50 states. It is bordered by Kentucky to th ...
, as well as athletic teams at the
University of Tennessee The University of Tennessee (officially The University of Tennessee, Knoxville; or UT Knoxville; UTK; or UT) is a public land-grant research university in Knoxville, Tennessee. Founded in 1794, two years before Tennessee became the 16th state ...
. Similarly, several Caribbean area codes were chosen as an alphabetic abbreviation of the country name.


Fictional telephone numbers

American
television program Television, sometimes shortened to TV, is a telecommunication medium for transmitting moving images and sound. The term can refer to a television set, or the medium of television transmission. Television is a mass medium for advertising, ...
s and films often use the central office code 555, or KL''amath'' 5 and KL''ondike'' 5 in older movies and shows, for fictitious telephone numbers, to prevent disturbing actual telephone subscribers if anyone is tempted to dial a telephone number seen or referred to on screen. Not all numbers beginning with 555 are fictional. For example, 555-1212 is the standard number for
directory assistance In telecommunications, directory assistance or directory inquiries is a phone service used to find out a specific telephone number and/or address of a residence, business, or government entity. Technology Directory assistance systems incorporate ...
. Only 555-0100 through 555-0199 are reserved for fictional use. Where used, these are often routed to information services; Canadian telephone companies briefly promoted 555-1313 as a pay-per-use "name that number" reverse lookup in the mid-1990s. Occasionally, valid telephone numbers are used as song titles. The 1962 Motown hit "
Beechwood 4-5789 "Beechwood 4-5789" is a song written by Marvin Gaye, William "Mickey" Stevenson and George Gordy. It was a 1962 hit single for the Motown girl group The Marvelettes on Motown's Tamla subsidiary record label. The song became a hit again when i ...
" was written by Marvin Gaye for the Marvelettes, while Stax/Volt Records'
Wilson Pickett Wilson Pickett (March 18, 1941 – January 19, 2006) was an American singer and songwriter. A major figure in the development of soul music, Pickett recorded over 50 songs which made the US R&B charts, many of which crossed over to the ''Bill ...
scored a soul hit in the 1960s with the similarly named " 634-5789". A more recent example is the
1981 Events January * January 1 ** Greece enters the European Economic Community, predecessor of the European Union. ** Palau becomes a self-governing territory. * January 10 – Salvadoran Civil War: The FMLN launches its first major offensiv ...
song "
867-5309/Jenny "867-5309/Jenny" is a 1981 song written by Alex Call and Jim Keller and performed by Tommy Tutone that was released on the album '' Tommy Tutone 2'', on the Columbia Records label. It peaked at No. 4 on the ''Billboard'' Hot 100 chart in May ...
" by Tommy Tutone, which was the cause of a large number of prank calls.


See also

* List of area code overlays * List of North American Numbering Plan area codes * Numbering Resource Utilization/Forecast Report


References


External links


North American Numbering Plan Administrator (NANPA)Canadian Numbering AdministratorNorth American Numbering Council

NANP Discussion 2003 Document - ''Understanding the North American Numbering Plan''
{{Telephone numbers International telecommunications Telephone numbers Telecommunications-related introductions in 1947