New Jersey actually had only the 201 area code for a few years after the dialing prefixes were established in 1947. When an entire state was covered by one area code, the middle digit was “0 ...

Area code 640 will be the tenth in the state, joining 201, 551, 609, 732, 848, 856, 862, 908, and 973. 201 was the first area code assigned to New Jersey in 1947.