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Interchangeable numbering plan area (NPA) codes and central office codes are codes that permit any of the ten numerals in the middle position of the area code and the central office code, which both are three-digit numbers. [1] [2] This change in numbering format was implemented first for central office codes by 1973, which eliminated the ...
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. 394 259-2653 is invalid, because the NANP is not assigning area codes with 9 as the second digit.
In the 1940s, the Bell System in the United States and Canada introduced a nationwide numbering system that identified central offices with a unique three-digit code, along with a three-digit numbering plan area code (NPA code or area code), making central office codes distinctive within each numbering plan area. These codes served as prefixes ...
Central office code protection. In the administration of the North American Numbering Plan, central office code protection is a numbering policy for maintaining local seven-digit dialing in communities that extend on both sides of the boundary line between multiple numbering plan areas (NPAs), such as in cross-border towns on state lines.
this was the first part of North America to have its code changed three times: from 213 to 714 1951: to 619 in 1982, and to 760 in 1997. was to have originally split off the portion of 760 serving San Diego County to a new 442 area code in late 2008/early 2009; that plan was cancelled. 2009: overlaid by 442. 761.
Several North American numbering plan areas (NPAs) were divided so that more office codes became available to smaller regions. However, as the growth accelerated, the Bell System decided to implement all-number calling (ANC) and to deprecate the use of central office names to provide more central office codes to each NPA. This extended the ...
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. [2] This increased the numbering pool for central ...
Telephone dial number card of c.1948 with the local telephone number 4-5876 in Atlantic City, NJ, using the central office prefix 4, later converted to AT4. Face of a 1939 rotary telephone dial with the telephone number LA-2697, which includes the first two letters of Lakewood, New Jersey, as the central office prefix, later converted to LA6.