Ten-digit dialing is a telephone dialing procedure in the countries and territories of the

North American Numbering Plan The North American Numbering Plan (NANP) is an integrated telephone numbering plan for twenty-five regions in twenty countries, primarily in North America and the Caribbean. This group is historically known as World Zone 1, World Numbering Zone ...

(NANP). It is the practice of including the

area code 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, rea ...

of a

telephone number A telephone number is the address of a Telecommunications, telecommunication endpoint, such as a telephone, in a telephone network, such as the public switched telephone network (PSTN). A telephone number typically consists of a Number, sequ ...

when dialing to initiate a

telephone call A telephone call, phone call, voice call, or simply a call, is the effective use of a connection over a telephone network between the calling party and the called party. Telephone calls are the form of human communication that was first enabl ...

. When necessary, the ten-digit number may be prefixed with the trunk code ''1'', which is referred to as ''1+10-digit dialing'' or ''national format''.

History

The implementation and expansion of the North American Numbering Plan between 1947 and 1992 preserved a long-standing practice in the United States and Canada that callers should only need to dial the local seven-digit telephone number when placing a call within the caller's exchange area or within the home numbering plan area (NPA). 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 ...

, callers dial the three-digit central office code and the four-digit station number of the destination telephone if it resides in the same numbering plan area. Dialing of an area code before the telephone number, referred to as ten-digit dialing, was only necessary for ''foreign NPA'' (FNPA) calls. Some communities with significant parts on both sides of an area code boundary implemented central office code protection, where possible, to ensure the same seven-digit local number was not assigned in two different area codes in the same city to assure seven-digit dialing in the entire community.

Code exhaustion relief

When the demand for telecommunication services in a numbering plan area threatens to exceed the capacity of telephone numbers of a single area code, the local public service agency and the Federal Communications Commission initiate relief measures to mitigate the exhaustion, and assure continued service with minimal customer impact in the affected areas.

Area code split

In an

area code split In telecommunications, an area code split is the practice of introducing a new telephone area code by geographically dividing an existing numbering plan area (NPA), and assigning area codes to the resulting divisions, but retaining the existing a ...

, the established practice of relief from 1947 to 1992, the affected numbering plan area is divided into suitable parts, most often two, and assigned a new area code to one of the areas, while maintaining the existing area code in the other. The area that retained the code was most commonly the denser-populated or geographically or historically more significant part. This freed the telephone numbers already issued in the new area for use in the existing, now smaller, numbering plan area. This practice preserved seven-digit dialing in all affected areas.

Area code overlay

By 1992, a new method of relief became available from the proliferation of electronic switching systems that were based on stored program control (SPC), which reduced the need for electromechanical extensions of the switching fabric. This made it possible to assign multiple area codes to a single numbering plan area. An area code overlay required additional technology in all affected switching systems to recognize the local area codes and select the appropriate routing for local calls, even within the wire center. This eliminated the possibility of maintaining seven-digit dialing, and required the dialing of ten digits for all calls. Consumer groups and some state regulators, such as the Illinois Commerce Commission and Citizens Utility Board for northwest Chicago, and the NYS Public Service Commission in NYC, opposed the requirement with attempts at litigation. The added effort in remembering and dialing longer numbers was perceived as a disadvantage of

overlay plan In telecommunications, an area code overlay complex is a telephone numbering plan that assigns multiple area codes to the same geographic numbering plan area (NPA). Area code overlays are implemented in territories of the North American Numbe ...

s, which were introduced to reduce the inconveniences associated with the traditional method of splitting an area. However, overlays have become the primary relief method and ten-digit dialing has become increasingly common in the U.S. and Canada.

1+10 dialing

Long-distance calls within a numbering plan area may also require dialing of an extra leading digit, designated as ''1+10D''. This became standard in all of North America by beginning of 1995 to allow introduction of interchangeable NPA codes, which are area codes that did not have a 0 or 1 as the middle digit and could therefore be confused with the central office code. Dialing ''1'' before the area code is most often required only for long-distance calls. Some telephone systems in early overlay areas do not accept a "1" before the area code for local calls; all Canadian landlines follow this pattern. However, in metropolitan

New York City New York, often called New York City (NYC), is the most populous city in the United States, located at the southern tip of New York State on one of the world's largest natural harbors. The city comprises five boroughs, each coextensive w ...

and

Chicago Chicago is the List of municipalities in Illinois, most populous city in the U.S. state of Illinois and in the Midwestern United States. With a population of 2,746,388, as of the 2020 United States census, 2020 census, it is the List of Unite ...

, as well as the entire state of

California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...

, the initial "1" is required even for local calls for landline phones located within an overlay complex or with a single NPA that also serves customers with a 988 NXX (see below). All cellphones in North America ignore this and only require the user to dial ten digits.

Ten-digit dialing in non-overlay areas

A few area codes not part of any overlay complex nonetheless require ten-digit dialing if part of the local calling area is within an overlay complex. For example, the

Fort Knox Fort Knox is a United States Army installation in Kentucky, south of Louisville and north of Elizabethtown, Kentucky, Elizabethtown. It is adjacent to the United States Bullion Depository (also known as Fort Knox), which is used to house a larg ...

Army An army, ground force or land force is an armed force that fights primarily on land. In the broadest sense, it is the land-based military branch, service branch or armed service of a nation or country. It may also include aviation assets by ...

base in

Kentucky Kentucky (, ), officially the Commonwealth of Kentucky, is a landlocked U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders Illinois, Indiana, and Ohio to the north, West Virginia to the ...

is served by area code 502, but its local calling area includes cities that are served by the 270/364 overlay complex. As a result, Fort Knox imposed ten-digit dialing for all off-base numbers when the 270/364 overlay was established in 2014. Area Codes US 10D changing L48

A July 2020 order by the

Federal Communications Commission The Federal Communications Commission (FCC) is an independent agency of the United States government that regulates communications by radio, television, wire, internet, wi-fi, satellite, and cable across the United States. The FCC maintains j ...

required ten-digit dialing of telephone numbers with area codes in the United States that were not overlaid, but had an assignment of the central office prefix ''988'', conflicting with its designation for the

National Suicide Prevention Lifeline The Suicide and Crisis Lifeline in the United States, or Suicide Crisis Helpline in Canada, and formerly known as the National Suicide Prevention Lifeline, is a suicide prevention and crisis help line to a network of a large number of crisis ce ...

by federal law. NANPA Planning Letter 544 cites 83 area codes affected in 37 states. Three additional area codes were already transitioning to ten-digit dialing as the result of overlay implementations. Central office code 988 was in the process of discontinuation for area code 904. While included in the list of 83 area codes,

area code 701 image:Area_code_ND.png, North Dakota numbering plan area and area code, with border states and provinces) poly 0 0 106 0 106 36 0 30 Area code 306 poly 109 1 107 34 239 35 298 32 297 0 Area code 204 poly 241 36 298 33 300 144 296 142 284 ...

in North Dakota will not be converted to ten-digit dialing because the 32 telephone numbers in the 988 central office were reassigned to another prefix. Several of these codes have subsequently been converted to overlay complexes and the implementation of such complexes could be expedited as the transition to ten-digit dialing was not necessary. As part of Canada's implementation of a national 9-8-8 hotline, the

Canadian Radio-television and Telecommunications Commission The Canadian Radio-television and Telecommunications Commission (CRTC; ) is a public organization in Canada tasked with the mandate as a regulatory agency tribunal for various electronic communications, covering broadcasting and telecommunic ...

(CRTC) announced in August 2022 that all remaining Canadian non-overlay areas with seven-digit dialing, most of which use "988" as a central office code under their respective area codes, were required to convert to ten-digit dialing by May 31, 2023. A partial exception was granted for the three northern territories served by area code 867, which was not projected to exhaust until at least 2043; only the

Yellowknife Yellowknife is the capital, largest community, and the only city in the Northwest Territories, Canada. It is on the northern shore of Great Slave Lake, about south of the Arctic Circle, on the west side of Yellowknife Bay near the outlet of t ...

area (which contains the 988 exchange) was required to convert, with seven-digit dialing remaining optional elsewhere in the region due in part to unique geographical and cultural considerations.

References

External links

* {{DEFAULTSORT:Ten-Digit Dialing North American Numbering Plan