Massachusetts was scheduled to receive two area codes under the original North American Numbering Plan proposal - the only state in New England to be split between two area codes. Area code 413 was intended for use in Pennsylvania . However, when area codes were finally assigned, the eastern two-thirds of the state (including Boston and Worcester) was assigned 617, with 413 in the west.
Due to the low population density of western Massachusetts, 413 remained in its original configuration even as the eastern portion of the state gained an additional three area codes from 1988 to 1997. As a result, 413 is the only original area code in Massachusetts that still maintains its original boundaries, and is one of the few original area codes (not counting those that cover an entire state) that has never been split or overlaid. Under current projections, it will stay that way in the foreseeable future. Despite the proliferation of cell phones and pagers (particularly in and around Springfield), 413 is nowhere near exhaustion. Despite this, 10-digit dialing is mandatory for some local calls outside 413.