Located in the Eastern (GMT -05:00) time zone. Area code 351 serves the state of Massachusetts. This area code was assigned on May 3rd, 2000. On May 2nd, 2001 it went into service. 351 is a General Purpose Code. 351 service area does overlap with 978 area codes. Dialing pattern for local calls within the same NPA (area code) is 10D.