Located in the Eastern (GMT -05:00) time zone. Area code 551 serves the state of New Jersey. This area code was assigned on April 2nd, 2001. On December 29th, 2001 it went into service. 551 is a General Purpose Code. 551 service area does overlap with 201 area codes. Dialing pattern for local calls within the same NPA (area code) is 10D. Calls between the 551 and 201 NPAs may be dialed as 10D.