Numbering plan area

Numbering plan areas and central offices

The new numbering plan divided the North American continent into regional service areas, termed numbering plan areas (NPAs). The divisions conformed primarily to the jurisdictional boundaries of the U.S. states and the Canadian provinces. Each NPA was identified by a unique three-digit code number, termed the numbering plan area code (NPA code, or short, area code), which was prefixed to the local telephone number when calling from one NPA to another. Calling within the same numbering plan area did not require dialing the area code, a feature today termed seven-digit dialing and today abandoned in numbering plan areas with multiple area codes. though 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.