Area codes 609 and 640
Area codes 609 and 640 serve telephones in central New Jersey, including the cities of Trenton, Princeton, Hamilton, and southeastern parts of the state and the Jersey Shore, including Atlantic City and Long Beach Island. In terms of geographic coverage, it is the largest in the state of New Jersey.
In the original North American Numbering Plan of 1947, all of New Jersey was a single numbering plan area, assigned the first of all area codes, 201. In 1958, it was split to create a second numbering plan area, 609. This division generally followed the dividing line between North Jersey, proximate to New York City, and South Jersey, proximate to Philadelphia and the Jersey Shore.
In 1999, the southwestern part of numbering plan area 609, the region adjacent to Philadelphia, was split off with area code 856. Since that time, the 609 territory covers parts of Central Jersey, South Jersey and the Jersey Shore, and many parts of Burlington County. It also includes portions of southern Middlesex County in Plainsboro, Cranbury, parts of South Brunswick and the extreme southern part of Monroe. The boundary was drawn in such a way so that several towns were divided between by area codes. Some prefixes assigned to mobile phone providers that lie within the 856 territory have never had their area code changed; thus 609/640 serves as a de facto partial overlay of 856, although it is rarely acknowledged as such.
As of October 2014, the area code 609 number pool was expected to be exhausted by the second quarter of 2017, about 15 months later than projected a year earlier. Permissive dialing began in mid-January 2018, and ended mid-August when 10-digit dialing became mandatory. In mid-September, new assignments of numbers with the 640 area code commenced.
