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Area code 510


Area code 510 is a California telephone area code that was split from area code 415 on September 2, 1991. It covers most eastern Bay Area cities in Alameda County (including the city of Oakland but excluding Dublin, Livermore, Pleasanton, and Sunol), and western Contra Costa County.

Area code 925 was created on March 14, 1998 from the eastern portion of the then 510 area code. The East Bay Hills serve as the rough dividing line.

In the United States, AT&T originally used area 510 for its TWX (TeletypeWriter eXchange) network. Western Union acquired the TWX network in 1969 and renamed it Telex II. By the 1970s, three TWX had been added (710 in the Northeast, 810 in Michigan, Ohio, Indiana, Kentucky, North Carolina, South Carolina, Georgia, Florida, Louisiana, Mississippi, and Alabama; and 910 west of the Mississippi). Each major city had one or more local exchange prefixes. Western Union upgraded the network to "4-row" ASCII operation (it previously used both "3-row" Baudot and ASCII transmission) and decommissioned the special TWX area codes in 1981.

In Canada, TWX used area 610 (all provinces) from 1962 until the remaining numbers were moved to area code 600 in 1992.


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