The California Public Utilities Commission predicts Santa Clara County’s 52-year-old area code, 408, will run out of numbers at the end of this year. Last October, the CPUC voted to add area code 669 to the same geographic region as the existing 408 area code in what is called an area code overlay. Starting Saturday, customers may dial ten digits for any number within the 408. On Oct. 21, a sure-to-be maddening voice recording will remind callers to dial a 10-digit number.