Washington state is getting a new area code in 2017.

An “area code overlay” is the addition of another area code to the same geographic region as an existing area code in order to meet the demand of new phone numbers. An overlay does not require customers to change their existing phone numbers. The newest area code in western Washington is 564. It will be available in areas currently covered under area codes 360, 206, 253, and 425 as those numbers run out.

The Utilities and Transportation Commission approved the initiative in May 2016 to address the need for additional numbers. In order to implement the new area code, 10-digit dialing for all western Washington area codes by the fall of 2017 will be required. This means callers must dial all 10 digits of a telephone number, including an area code, when making local phone calls.

The North American Numbering Plan Administrator projects the 360 area code will be out of numbers by early 2018.

The commission originally approved the area code overlay for western Washington in 2000, but postponed it after successful state and national number conservation efforts.

“As part of the plan, western Washington telephone service providers must implement a comprehensive education program to inform customers of the new dialing requirement. This includes customer education, community involvement, and media outreach,” said a UTC press release.

According to Kiro7 News, T-Mobile notified its customers on Dec. 28. It’s online information materials say, “Beginning Jan. 28, 2017, you should start using the new dialing procedure whenever you place a call from the 206, 253, 360, and 425 area codes. If you forget and dial 7 digits, your call will still be completed. Beginning July 29, 2017, you must use the new dialing procedure, as described above for all local calls. After this date, if you do not use the new dialing procedure, your call will not be completed and a recording will instruct you to hang up and dial again. Beginning Aug. 28, 2017, new telephone lines or services may be assigned numbers using the new 564 area code.”