Original North American area codes

The original North American area codes were established by the American Telephone and Telegraph Company (AT&T) in 1947. The assignment was in accord with the design of a uniform nationwide telephone numbering plan that supported the goal of dialing any telephone in the nation without involvement of operators at each routing step of a telephone call from origination location to its destination. The new technology had the aim of speeding the connecting times for long-distance calling by eliminating the intermediary telephone operators and reducing cost. It was initially designed and implemented for Operator Toll Dialing, in which operators at the origination point would dial the call as instructed by service subscribers, but had also the benefit of preparing the nation for Direct Distance Dialing (DDD) by customers years later. The nationwide and continental application followed the demonstration of regional Operator Toll Dialing in Philadelphia during the World War II period.

The new numbering plan established a uniform destination addressing and call routing system for all telephone networks in North America which had become an essential public service. The project mandated the conversion of all local telephone numbers in the system to consist of a three-character central office code and a four-digit station number.

The initial "Nationwide Numbering Plan" of 1947 established 86 numbering plan areas (NPAs) that principally conformed to existing U.S. state and Canadian provincial boundaries, but 16 states and provinces were subdivided further. Forty NPAs were mapped to entire states or provinces. Each NPA was identified by a three-digit area code used as a prefix to each local telephone number.