Area code 206

Area code 206 is a North American telephone area code in the U.S. state of Washington assigned to the numbering plan area (NPA) that includes the city of Seattle, Shoreline, Lake Forest Park, the islands of Mercer, Bainbridge, and Vashon, and portions of metropolitan Seattle from Des Moines to Woodway.

This numbering plan area is one of the few urbanized areas in the North American Numbering Plan without a code overlay, meaning telephone calls within Seattle may still be originated by seven-digit dialing. The area code 564 overlay will be activated in 2017, with ten-digit dialing required by mid year.

Area code 206 was one of the original area codes assigned in 1947. The original numbering plan area was the entire state of Washington. On January 1, 1957, area code 509 was assigned for the eastern two-thirds of the state in a flash-cut, with the split roughly following the Cascade Mountains. On January 15, 1995, most of the old 206 territory outside of the Seattle-Tacoma area split off with area code 360, which was one of the first two area codes not conforming to the N0X/N1X format.

...
Wikipedia