Heads up to the 510: East Bay's new 341 area code officially in effect

It's here: On Monday the East Bay officially implemented its new 341 area code.

The new numbers serve as an overlay to the 510 region to ensure a continuing supply of telephone numbers for the area, according to the California Public Utilities Commission.

In June, the CPUC ordered a new overlay for the in the 510 which covers Alameda and Contra Costa counties. Using the new 341 area code became mandatory as of Monday, as carriers will now officially be able to assign numbers to the new code. 

The overlay will not require customers to change their existing area code, but customers will have to dial "1" before the three-digit area code for all calls from telephone numbers with a 510 code. The 341 will co-mingle with the 510 code in the western parts of Alameda and Contra Costa counties, CPUC officials said. 

Ahead of the implementation of the new code, CPUC officials advised residents and businesses to reprogram any equipment or alarm systems to dial "1" before the area code, test telephone equipment and update items like checks, business cards and advertisements to reflect the change.

If callers don't use the new procedure, they'll get a recorded message instructing them to hang up and try it again. People can still dial 911 and other three-digit numbers, like 311 and 411, without first dialing "1." 

The new area code was added in anticipation that the 510 will run out of available prefixes before the end of the summer. (The prefix is the first three numbers that come after the area code.) Almost 8 million numbers are already assigned to 510. 

The 510 area code came into existence in 1991, when it was split off from the 415 area code. The 510 was split again in 1998, when the new 925 area code came into existence on the east side of the East Bay hills.