In 1947, the American Telephone and Telegraph Company (AT&T) devised the first nationwide telephone numbering plan and assigned the original North American area codes. The state of California was divided into three numbering plan areas (NPAs) with distinct area codes: 213, 415, and 916, for the southern, central, and northern parts of the state, respectively.[1]
In 1949, Oakland, CA, received the fifth regional dial switching center for Operator Toll Dialing in the nation,[2] which set the stage for direct distance dialing by customers in the 1950s. In 1950, the boundaries of the California numbering plan areas were redrawn to produce a division of the northern and central parts along a north–south-running dividing line. Numbering plan area 415 became the coastal region from the North Coast to the Oregon border, while 916 was redrawn to comprise the northeastern corner of the state.[3] This realignment resulted in Sacramento changing from area code 415 to 916, and Bakersfield to 213.
During the initial trials of DDD, starting in 1951, area code 318 was temporarily installed for the new toll-switching center in San Francisco to separate calls destined through Oakland (415), as six-digit translation was not available until two years later.
In subsequent decades the California numbering plan areas underwent many area code splits and area code overlay arrangements. As of March 2025, California has 41 active area codes.