Area codes 978 and 351 are telephone area codes in the North American Numbering Plan for north central and most of northeastern Massachusetts.
Area code 978 was created in an area code split of area code 508 on September 1, 1997. A permissive dialing period ended on February 1, 1998. Area code 351 was added to the same service area in an overlay complex on May 2, 2001. Since then, ten-digit dialing dialing has been mandatory for all telephone calls.
Prior to when this area was served by 508 (July 1988), it was served only by area code 617, along with the rest of the eastern two-thirds of the state. Some mobile phone numbers from the 1990s assigned to rate centers in 978 and 351 kept the 508 area code just on those mobile lines after it was split.
The numbering plan area is part of local access and transport area (LATA) 128.