In the original configuration of the first nationwide telephone numbering plan of 1947, all of New Jersey was a single numbering plan area (NPA), assigned the first of all area codes, 201. By 1956, it was split to create a second numbering plan area, 609.[1]
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.
[2] Despite the division into two numbering plan areas, all calls within the state of New Jersey were dialed without area codes until July 21, 1963.[3][4][5]
This configuration of two area code in New Jersey remained in place for c. 35 years, until 1991, when the 201 numbering plan area was further divided to create area code 908 in its southern half. This made available more central office prefixes in the northern part, comprising the densely populated western suburbs of New York City, as well as in the area south of Newark, which fell into NPA 908.
On June 1, 1997, services growth in numbering plan area 908 required splitting the area with a new area code 732 assigned to its southeastern half, along the Atlantic seaboard.[6] Following a six month grace period, the use of the 732 area code became mandatory on December 6 of that year. The area includes Middlesex, Somerset, and Union counties in Northern and Central New Jersey, and Monmouth and northern Ocean counties on the New Jersey Shore.
The assignment of area code 848 to the same numbering plan area in 2001 created an overlay complex for this region, after the pool of 732-numbers began to exhaust rapidly.[7]