Area codes 510 and 341

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Map of California numbering plan areas (blue) and border states. Area code 510 is shown in red.

Area code 510 is a California telephone area code serving most of the East Bay. It split off from area code 415 on September 2, 1991.[1] It covers most of Alameda County (including the city of Oakland but excluding Dublin, Livermore, Pleasanton, and Sunol), and western Contra Costa County.

Area code 341 has been assigned as an overlay area code for the region covered by 510 and will serve as California's 35th area code; it will be available for use in new phone numbers starting approximately July 2019 throughout the entire area where 510 is already in use. This would ease customers from the burden & expense of changing numbers.[2][3] Area code 925 was created on March 14, 1998 from the eastern, inland portion of what was then 510's territory; the East Bay Hills serve as the rough dividing line between 510/341 and 925.

Cities in the 510 area code[edit]

Alameda County[edit]

Contra Costa County[edit]

Prior usage for TWX[edit]

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 TWXs 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.[4] 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 610 (nationwide) from 1962 until the remaining numbers were moved to area code 600 in 1992.

Introduction of 341[edit]

510 is projected to run out of available central office prefixes (the first three numbers after the area code in a U.S. phone number) by the second quarter of 2019. In response to this problem, the California Public Utilities Commission held meetings in Berkeley, Oakland and Hayward in January and February 2017 to discuss area code relief for 510.[2] The North American Numbering Plan Administrator, which manages area codes throughout North America, proposed in May 2017 that CPUC relieve 510 by introducing a new overlay area code, 341, which would be assigned in addition to 510 throughout all of 510's territory. NANPA had previously assigned 341 as the relief area code for 510 in 1999, but nationwide number pooling procedures eliminated the need for a new area code at that time, so NANPA retained 341 for the then-future relief of 510.[5] CPUC accepted NANPA's proposal in a decision on June 21, 2018.[3] Once the 341 overlay on 510 takes full effect in July 2019, customers in the 510 area can be assigned either 510 or 341 phone numbers, and will be required to dial the area code even to call other 510/341 numbers (10- or 11-digit dialing).[6]

See also[edit]


  1. ^
  2. ^ a b Prosper, Terrie (June 21, 2018). "CPUC Provides More Numbers in 510 Area Code Region" (PDF) (Press release). California Public Utilities Commission. Retrieved June 21, 2018.
  3. ^ a b California Public Utilities Commission (June 21, 2018). "Decision Granting Request for an All-Service Area Code Overlay in the 510 Numbering Plan Area" (PDF). Retrieved June 21, 2018. (The decision states that 341 should be fully adopted 13 months after the date of decision, which is July 2019.)
  4. ^ Traffic Routing Guide, sec. 15-16, AT&T, 1975
  5. ^ North American Numbering Plan Administrator (May 19, 2017). "Application of the North American Numbering Plan Administrator, On Behalf of the California Telecommunications Industry, For Relief of the 510 Numbering Plan Area" (PDF). Retrieved June 21, 2018.
  6. ^ Avalos, George (June 21, 2018). "341 is the East Bay's new telephone area code, joining 510, 925". The Mercury News. Retrieved June 21, 2018.

External links[edit]

California area codes: 209, 213/323, 310/424, 341/510, 408/669, 415/628, 442/760, 530, 559, 562, 619, 626, 650, 657/714, 661, 707, 747/818, 805, 831, 858, 909, 916, 925, 949, 951
North: 707
West: 415/628, 650 area code 510/341 East: 925
South: 408/669

Coordinates: 37°42′N 122°06′W / 37.7°N 122.1°W / 37.7; -122.1