From 1947 to 1957, all of Washington state was assigned
area code 206 for routing long-distance telephone calls in
Operator Toll Dialing. In 1957, the numbering plan area (NPA) was reduced to just
Western Washington, with most of
Eastern Washington (east of the
Cascade Mountains) receiving
area code 509. Washington remained with two NPAs for 38 years. This configuration was unchanged even with western Washington's explosive growth in the second half of the 20th century and the proliferation of cell phones, fax machines, and pagers. By the early 1990s, the ensuing resource pressure meant that the need for additional central office prefixes and telephone numbers could no longer be staved off. Accordingly, of the region outside the Seattle and Tacoma areas was split from 206 to form a new numbering plan area with area code 360. Numbering plan area 360 comprises two sections that resulted from numbering disputes in the community. The configuration arose when residents of several Seattle exurbs protested their move from the more-established 206 to the new area code. In response,
US West returned some central offices in these exurbs to 206. However, 206 was on the brink of exhaustion even after the creation of 360. The restoration of these exurbs forced the
Washington Public Utilities Commission to switch most of Seattle's suburban ring into areas
253 and
425 in 1998, sooner than originally planned. This made 360 one of the few NPAs in the North American Numbering Plan without a continuous land border; others include
706 in Georgia,
423 in Tennessee and
386 in Florida. In 1999, the
Washington Utilities and Transportation Commission intended to overlay 360 with an additional area code, but the implementation was delayed indefinitely. A 2016 report forecasted exhaustion in 2018. The change was finally approved in May 2016. On August 28, 2017 numbering plan area 360 was assigned the second area code, 564, to form an
overlay numbering plan. Area code 564 is intended to eventually overlay other western Washington NPAs (206, 253, and 425) when demand requires numbering relief action. the first 564 prefix was assigned in 2021 360 prefix was assigned on October 22, 2021. Area codes 360 and
334 (Alabama), which began service on the same day, were the first two
interchangeable NPA codes in the North American Numbering Plan, having a middle digit other than 0 or 1. ==Service area==