Area Codes and Numbering

The North American Numbering Plan (NANP) is the telephone numbering system for the Public Switched Telephone Network in the United States, Canada, and some Caribbean countries. The NANP is divided into smaller Numbering Plan Areas that are each identified by a three-digit code, commonly known as an area code. Telephone numbers in the NANP are structured in the format NPA-NXX-XXXX, in which

 
NPA is the 3-digit area code that identifies a specific geographic area;

 
NXX is the 3-digit prefix that identifies a specific central office within an area code; and

 
XXXX is the 4-digit line number that identifies a specific line within a central office.

 
The Federal Communications Commission (FCC) has exclusive jurisdiction over telephone numbering in the United States but has delegated specific authority to state regulatory agencies. Tasked with the authority granted by the FCC, the CPUC conducts area code relief and implement number conservation measures in accordance with FCC policy.

 
As of September 2018, California has 34 area codes. A new area code is introduced to a geographic area when there are no more three-digit prefixes available in the existing area code.

 
In recent years, growing consumer demand for advanced technologies and smart devices has led to increasing consumption of telephone numbers. As a result, telephone prefix shortage has occurred in many locations, resulting in the need to add new area codes.

Area codes are introduced in the form of a geographic split or an overlay. In the last ten years, California has introduced ten area codes using the overlay method.

On June 21, 2018, the CPUC ordered an overlay for the 510 area code in Alameda and Contra Costa Counties.  The new 341 area code will be introduced on July 22, 2019.  The 909 area code is the next area code to be depleted of available prefixes.  The 909 area code is projected to run out of available prefixes by September 2021.