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.

As of January 2017, this numbering plan area was one of the last urbanized areas in the North American Numbering Plan without a code overlay, meaning telephone calls within Seattle could still be originated by seven-digit dialing. The area code 564 overlay was activated on January 28, 2017, and ten-digit dialing became required on July 29, 2017.

History
Area code 206 was one of the original area codes assigned in 1947, and originally covered the entire state of Washington. On January 1, 1957, area code 509 was assigned for the eastern two-thirds of Washington in a flash-cut, with the split roughly following the Cascade Mountains.

Despite western Washington's explosive growth in the second half of the 20th century, this configuration remained in place for 38 years. By the start of the 1990s, however, 206 was on the brink of exhaustion due to the Seattle area's continued growth, as well as the proliferation of cell phones, pagers, and fax machines. The supply of numbers was further limited because much of the southern portion of the old 206 territory (Vancouver, Centralia, Kelso, etc.) is part of the Portland LATA, meaning many numbers in Portland's area code 503 weren't available for use.

Finally, on January 15, 1995, most of the old 206 territory outside of the Seattle/Tacoma area split off as area code 360, which was one of the first two area codes not conforming to the N0X/N1X format.

Numerous residents in the Seattle exurbs protested about no longer being associated with 206, leading US West, now part of CenturyLink, to reintegrate those areas shortly after the split.  As part of the reintegration, the cities of Des Moines and Woodway were both split between the new area codes due to capacity at switching centers.

However, 206 was on the brink of exhaustion even after the 360 split. The return of these exurbs, combined with the continued proliferation of cell phones, faxes, and pagers, hastened a three-way split of the 206 territory, effective on April 25, 1997.  The southern portion, including Tacoma, received area code 253, while the northern portion, including Everett and the Eastside, was assigned area code 425.