The 510 area code, which covers western portions of Alameda and Contra Costa counties, is expected to use up its available suffixes by June 2018.

Telecommunications service providers recommended that California Public Utilities Commission, or CPUC, use the overlay method, meaning it will add a new area code in the region, in addition to the 510 area code. The plan, pending CPUC approval, would add a new area code by December 2017, according to CPUC’s website.

“The desired method these days is to do an overlay,” said Joe Cocke, senior numbering plan administration relief planner for the North American Numbering Plan Administration, or NANPA, a third-party administrator that forecasts when area codes will be exhausted. “All the current customers keep their existing telephone number and area code.”

After the overlay is implemented, there will be a six-month grace period, during which you can type a seven-digit phone number, not including the area code, and the call will still go through. Subsequently, however, residents will need to dial a ten-digit number to contact another person with either a 510 area code or the new area code.

The 510 area code was created in 1991 after it split from the 415 area code. In 1998, the 925 area code split from the 510 area code.

According to John Votava, a public relations representative for Sprint, overlays are common because of the growing demand for mobile devices, and the company is prepared for the implementation of any new area codes.

While Cocke did not release the new area code, he said NANPA reserves codes several years ahead of an anticipated exhaustion and tries to introduce area codes that are not similar to those of adjacent regions to minimize customer confusion.

“Area codes define communities in the Bay Area,” said a Sprint employee, who asked to remain anonymous because they are not allowed to comment on behalf of the company. “A lot of people are very passionate about being a 415-er or a 510-er.”