Area codes 510 and 341 are telephonearea codes in theNorth American Numbering Plan (NANP) serving much of theEast Bay in the U.S. state ofCalifornia. The numbering plan area (NPA) includes parts ofContra Costa County and westernAlameda County, including the city ofOakland, but excludesDublin,Livermore,Pleasanton, andSunol. Area code 510 was established in 1991 in a split ofarea code 415, and 341 was added to the numbering plan area in 2019.
Area code 510 was established on September 2, 1991, in anarea code split of the415 numbering plan area.[1] On March 14, 1998, the inland portion of the East Bay was split off witharea code 925. The dividing line followed theBerkeley Hills; almost everything west of the hills stayed in NPA 510, while everything east of the hills received the new area code.
By 2016, theCalifornia Public Utilities Commission (CPUC) projected that NPA 510 would exhaust its numbering pool by the second quarter of 2019. In response, the commission held mitigation meetings in Berkeley, Oakland, and Hayward in January and February 2017.[2] TheNorth American Numbering Plan Administrator (NANPA) proposed in May 2017 anoverlay complex for the numbering plan area with new area code 341. NANPA had previously assigned 341 as the relief area code in 1999, but nationwidenumber pooling procedures eliminated the need at that time. The NANPA retained 341 for the then-future relief of 510.[3] CPUC accepted the relief plan on June 21, 2018.[4] With the start of the overlay in July 2019, customers in the numbering plan area can be assigned telephone numbers with either code, and must dial the area code for all calls.[5][6]
New central office codes in 341 became available on July 22, 2019.[2][4]Ten-digit dialing became mandatory in the East Bay a month earlier, on June 22.[7]
In 1962,AT&T assigned NPA 510 for conversion to dial service of theTeletypewriter Exchange Service (TWX) in the United States.[8][9] Telex use of area code 510 was decommissioned in 1981 after conversion of the service to new transmission technologies byWestern Union.
The service area contains the following cities in two counties.
{{cite web}}: CS1 maint: archived copy as title (link)| North:369/707 | ||
| West:415/628,650 | 341/510 | East:925 |
| South:408/669 |