The demand for new phone numbers is forcing ten-digit dialing into the South Bay, starting on Saturday, October 20th. If your number has a 408 area code, you will have to dial 1, the area code and the number to make a call even to another 408 number, or the call will not go through.

California's Public Utilities Commission is blending in a new area code, 669, using what's called an "overlay" of 408's territory. That region includes Santa Clara County and adjoining slivers of Alameda and Santa Cruz Counties. (See page 5 of this link for a map).

Regulators decided on an overlay, which allows everyone to keep their existing numbers, rather than splitting the area codes geographically. That would have created a new area code south of San Jose.
 
"So those people living in Morgan Hill would've had to change their phone numbers completely," says CPUC spokesman Chris Chow.  "Under the overlay, you will keep your existing phone number now, plus the area code."

In the past regulators have considered adding area codes to San Francisco, the Peninsula and the North Bay, but those plans are canceled. An analysis from the CPUC of California's area codes shows that San Francisco's 415 has enough numbers left to last about another three years. 650 on the Peninsula should last until 2028, 707 is good through 2026, and 510 in the East Bay should last until about 2023.