List of original NANP area codes

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In preparation for direct distance dialing, AT&T and the Bell System created the North American Numbering Plan in 1947. The plan divided the United States and Canada into numbering plan areas (NPAs) and assigned a three-digit prefix to each.

Initially the codes were used only by long-distance operators; the first customer-dialed call using an area code was placed on November 10, 1951, from Englewood, New Jersey, to Alameda, California.[1] Local subscriber numbers were standardized to seven digits, which included a two-letter exchange name and five digits. Direct dialing was gradually implemented throughout the continent and by the mid-1960s, direct distance dialing was commonplace in most larger cities.

The list of original North American area codes assigned 86 area codes, with the most prominent, frequently called population centers being assigned sequences with the shortest dial time on rotary dial telephones.[2] New York City was assigned 212, Los Angeles 213, Chicago 312, and Detroit 313.

In the original plan, the second digit of all area codes was either 0 or 1, to avoid conflicts with local telephone exchange prefixes, which were assigned one of the digits 2 through 9 in the second position. Codes with a middle digit of 0 (zero, ten dial pulses) were initially assigned to area codes which covered an entire state or province; area codes having 1 (one, a single pulse) as the second digit were assigned to states or provinces that were divided into multiple area codes.

Long distance calls within the same area code could originally be made with eight digits, by dialing 1 and the seven-digit local number. As this system relied on the second digit to distinguish area codes (0 or 1) from local exchanges (2–9), exchange numbers which didn't follow the pattern would break 1 plus seven digit calling within an area code and force 1+10D to be dialed for all toll calls from that area. As allowing digits other than 0 or 1 into the second area code digit would break 1+7D toll calls throughout the NANP, requiring '1' and the area code for all toll calls, these were not issued until 1995.

No codes ending N00, N10 or N11 occur in the original set. The N00 series were used for non-geographic numbers (starting with intrastate toll-free +1-800 numbers in 1966), N10 were originally teletypewriter exchanges and N-1-1 remains reserved for information and emergency numbers.

List of original area codes[edit]

See also[edit]