Get ready to hang up on the 408, and start dialing 669.

Why? We’re simply running out of numbers.

State regulators Thursday gave final approval to a plan to replace the South Bay’s longtime area code for new phone lines. Everyone in the 408 area code will keep their current numbers, area code and all, but two key changes are starting:

Those three little numbers have been synonymous with Silicon Valley and its identity for more than 50 years. But the approval granted by the California Public Utilities Commission will send 4, 0 and 8 to the vintage pile along with VHS tapes, typewriters and record players.

So in the past year the obscure group in charge of such matters — the North American Numbering Plan Administration — has introduced us to 6, 6 and 9.

But it’s been a long time coming. The 408 has been officially “in jeopardy” of running out of digits since 1998, setting up a number “rationing” process that made the South Bay the area code’s exclusive home, though the abundance of cellphones in the nation’s tech capital has accelerated its death. Now, there are 8 million 408 numbers either in use or reserved for businesses and less than 50,000 available numbers left, just enough to get through early 2013.

The new number is believed to have been drawn at random, as far as anyone knows.

The 669 area code is expected to last 36 years, attaching itself to the next generations of techies, families and students from around Santa Clara County and very small portions of neighboring Alameda and Santa Cruz counties.

The commission’s vote ends a small debate over who gets which area code. Another proposal would have split the region into two area codes, with some getting 408 numbers and others receiving 669, but that was deemed too confusing and an unnecessary hardship to people and businesses that would have had to change their numbers.

“With (the option chosen), no one has to change their telephone number, a result that is particularly appealing to me, since small businesses are facing such great economic challenges in this economy to stay competitive and cost-effective,” Commissioner Timothy Simon said in a statement.

It’s not the first time the region has changed an area code. The 415 area code now attached to San Francisco was originally also assigned to all South Bay callers in 1947, before that, too, became endangered from overuse, and the 408 was launched in 1959. Then in 1999, San Benito County and most callers in Santa Cruz and Monterey counties lost the 408 area code as part of the plan to extend it as long as possible.

Contact Mike Rosenberg at 408-920-5705.