Area code 564 is an area code for the state of Washington covering all of Western Washington, including Seattle. It is an overlay plan for area codes206, 253, 360, and 425. It was originally proposed and approved in 2000, but it was not implemented until July 29, 2017. Initially, it was implemented as a concentrated overlay for the 360 area, comprising all of western Washington outside of the core of the Seattle/Tacoma metropolitan area. While it will expand to other area codes in the region as they exhaust, its implementation has made ten-digit dialing mandatory in all of western Washington. In 1999, area code 564 was proposed as an overlay of 360. That version of the overlay was slated for implementation on July 29, 2000. Later, the Washington Utilities and Transportation Commission determined that the actual increase in need for new numbers in 360 had fallen short of projections and so it postponed the overlay until at least February 2001. In May 2000, the commission projected that the metropolitan Seattle area codes would also soon exhaust their number pools, and it expanded the 564 plan to include those areas as well. By the summer, however, that was determined not to be immediately necessary. The overlay was then planned for application on October 20, 2001. On August 22, 2001, the WUTC announced that increased efficiency in the reuse of the existing number pool meant that the immediate need for the new area code had subsided. Part of that was also attributed to a downturn in the telecommunications sector. The commission put off implementation until no earlier than October 20, 2002. Since the development of the initial plan for the area code, the WUTC and the NANPA have rebuffed the telephone companies' request for a new area code and instead directed them to actively share and efficiently use the number blocks that had already been assigned. That refers mainly to the practice of number pooling, which divides telephone exchange prefixes for more efficient allocation as 10 blocks of 1,000 numbers, instead of assigning a prefix's whole numbering space to one carrier in the one rate center. The WUTC took further steps to decrease the need for new number blocks in 360 and 509 and head off the need for new area codes, including aggressive reclamation of unused and underused number blocks and exchanges. The introduction of mandatory local and wireless number portability has also served to stem the demand for new numbers and thus new area codes. According to the WUTC's estimate as of 2014, the earliest projection for any Western Washington area code to be exhausted is 2018 for area code 360. The other codes are not expected to exhaust before 2025. On July 29, 2017, ten-digit dialing became mandatory for all local calls in Western Washington, replacing the use of seven-digit dialing. Until then, Seattle had been one of the few major American cities with seven-digit dialing still functioning. Since September 30, 2017, telephone numbers with the area code 564 are issued in the existing number plan area 360. Once other codes in Western Washington are exhausted, 564 numbers will be assigned in those areas also.
