List of original NANPA area codes

This is the list of original North American Numbering Plan area codes of 86 plan areas as defined by AT&T in 1947.

In preparation for direct distance dialing, AT&T and the Bell System developed the North American Numbering Plan in the 1940s. The plan divided the United States and Canada into numbering plan areas (NPAs) and assigned a three-digit dialing prefix to each. Over the course of the decade following introduction of these routing codes, local subscriber numbers were standardized to seven digits. This included a three-digit central office prefix, dialed as the first two letters of the local central office name and one digit, and the four-digit subscriber station number.

The first digit of the area code was never 0 or 1, as a single leading pulse (1) was ignored by most switching equipment, and 0 could be confused with requests for an operator or the long-distance desk. The original numbering plan defined the second digit of all area codes as either 0 or 1, to distinguish them from the central office codes, which always used a letter in the middle position, as letters were mapped on the dial only to digits 2 through 9. Area codes with the middle digit 0 were assigned to numbering plan areas that covered an entire state or province, while jurisdictions with multiple plan areas received area codes having 1 as the second digit.

No codes of the form N00, N10 or N11 occurred in the original area code allocation, where N is 2 through 9. The series N00 was used for non-geographic numbers, starting with intrastate toll-free 800-numbers in 1966.N10 numbers were originally teletypewriter exchanges and N11 remains reserved for information and emergency numbers. No codes were originally assigned to Alaska or Hawaii, as neither were US states at the time, or to Puerto Rico.

Initially, the numbering plan area codes were used in Nationwide Operator Toll Dialing by long-distance operators for placing trunk calls. Preparations proceeded for end-customer direct distance dialing (DDD) and while the first customer-dialed call using an area code was placed on November 10, 1951, from Englewood, New Jersey, to Alameda, California. it took until the 1960s until direct distance dialing was commonplace in most cities.

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