Area codes 415 and 628
Area codes 415 and 628 are telephone area codes in the North American Numbering Plan (NANP) for the city of San Francisco and its northern suburbs in Marin County (across the Golden Gate), and the northeast corner of San Mateo County. Area code 415 was one of the eighty-six original North American area codes established in 1947, but modified in geographic configuration later. Area code 628 was assigned in 2015 to form an overlay in that numbering plan area in mitigation of central office prefix exhaustion. History. When the North American Numbering Plan was  installed by AT&T for Operator Toll Dialing in 1947, the state of California was divided into three numbering plan areas (NPAs) arranged as geographical zones in the southern part, the central part, and the northern part of the state. Area code 415 was assigned to central California, south of area code 916, and north of area code 213. It stretched from Sacramento in the north to Bakersfield in the south. In 1950, the boundaries of the numbering plan area 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. As part of this realignment, Sacramento was renumbered from area code 415 to 916, and Bakersfield to 213. With the preparations for nation-wide direct distance dialing (DDD) in the early 1950s, area code 318 was temporarily used in the San Francisco area, initially by customers in Englewood, New Jersey, participating in the first customer trials to reach the city, as well as some areas north of the Golden Gate. In 1953, the entire  Bay Area was "reunited" in using area code 415. Area code 415 has been split three times due to the Bay Area's rapid economic growth and demand for telecommunication services: On February 21, 2015, the numbering plan area was transitioned to an overlay plan by adding area code 628 to the same service area for new numbers, making ten-digit dialing mandatory in the area, with eleven-digit dialing necessary from landlines.