Area codes 617 and 857 are telephone area codes in the North American Numbering Plan (NANP) for the U.S. state of Massachusetts, serving the city of Boston and several surrounding communities such as Brookline, Cambridge, Newton and Quincy. Area code 617 is one of the original North American area codes created in October 1947, when it served the eastern two-thirds of Massachusetts, from roughly the western end of Worcester County to Cape Cod and the South Coast. History Massachusetts was the only New England state divided into multiple numbering plan areas (NPAs) when the American Telephone and Telegraph Company (AT&T) devised the first nationwide telephone numbering plan in 1947. Its most populous part, the eastern half received area code 617, while the rest of the state was served by area code 413. In July 1988, most of the western, northern, and southern portions of the old 617 territory, including Worcester County, the Merrimack Valley, the South Coast, and the Cape and Islands, were split off as area code 508. Permissive dialing of 617 continued across eastern Massachusetts until January 1, 1989. In 1997, the northern, western and southern portions of the new 617 split off as 781, which almost completely surrounds 617. This reduced 617 to Boston itself and its closest neighboring communities. This was intended as a long-term solution, but within three years 617 was close to exhaustion once again due to the demand for more phone lines for auxiliary devices (mobile phones, fax machines, pagers, and BBS lines). On May 2, 2001, 857 was overlaid onto 617. Since then, 10-digit local dialing has been mandatory. Some mobile telephone numbers from the 1990s assigned to communities in the area surrounding 617 (which is now the 781 area code) kept the 617 area code after the split. Area code 508 was split from 617 on July 16, 1988. Area code 978 subsequently split from 508 on September 1, 1997. Area code 781 was split from 617 on September 1, 1997. As of 2018, the 617/857 NPA is projected to be exhausted by 2041. Service area Counties The numbering plan area 617/857 includes portions of the following counties: Essex Middlesex Norfolk Suffolk Communities It includes the following communities: Belmont Boston Brookline Cambridge Chelsea Everett Milton Newton Quincy Somerville Watertown Winthrop Central office codes by location The NPA includes central offices with the following prefix format 617-NXX: Belmont: 209, 404, 484, 486,