Beginning this Saturday, you'll have to dial three more numbers before making a local call in San Antonio.
Right now you can dial a local number in San Antonio without using the area code 210. So instead of 555-5555, you'll need to dial 210-555-5555.
The rules change again next month.
Beginning October 23, phone providers will start issuing a second area code for Bexar County: 726. That means you'll have to dial 210 or 726 first, depending on the number.
So why the change?
"One area code can handle about 7.9 million phone numbers. And when those are exhausted, it's time for a new one," said Terry Hadley, a spokesman for the Texas Public Utility Commission.
The Public Utility Commission, which oversees the process, says that some 210 numbers will still be available, for now.
"While landlines, traditional landlines are decreasing, more and more people have cell phones. Often a family may have three or four different phone numbers or more with all the mobile phones everyone has and that puts a load on the existing numbers," Hadley said.
If you're calling from a landline, you may be required to dial 1 before the area code.
Alarm systems and office equipment, like a fax machine, may also need to be re-programmed.
For specific questions, contact your phone provider.