In 1947, when area codes were introduced to California, the locality now served by the 408 area code was part of the 415 area code, one of the first three area codes in the state. In June 1959, the 408 area code was created by splitting the 415. In 1999 San Benito County and most of Monterey County and Santa Cruz County were split from the 408 and assigned the 831 area code.
The 408 area code currently includes eleven rate centers in Santa Clara County and in small portions of Alameda, Santa Cruz, and Stanislaus Counties. Most of the 408 area code is contained within the San Jose Metropolitan Statistical Area (MSA).
In 1997 the North American Numbering Plan Administrator (NANPA) determined that the 408 area code was running short of numbers. In response to the NANPA’s petition, the CPUC approved an area code overlay on November 19, 1998. The 408 overlay was scheduled for January 1, 1999, with mandatory 1 + 10 digit dialing to begin on October 1, 1999.
In December of 1999, Decision 99-12-051, the CPUC suspended all approved overlays, including the overlay previously ordered in the 408 area code. In 2001, the FCC required service providers to engage in mandatory number pooling, and the CPUC instituted mandatory number pooling in California. The pooling process allows service providers to share codes, which are blocks of 10,000 numbers distinguished by a unique three letter code commonly called a prefix.
Since that time, the CPUC has pursued number conservation, prodding service providers to return unused numbering resources. Number conservation has allowed the 408 to provide adequate number resources to serve all telecommunications service providers until October 2012.