Area code 351 is an overlay of 978 in northeastern Massachusetts, including cities such as Lowell, Lawrence, Peabody, and Fitchburg. It was introduced in 2001 due to the depletion of available numbers in the 978 area, and ten-digit dialing became mandatory. This area is known for its rich industrial history, vibrant immigrant communities, and its role in the Greater Boston commuter belt. While 978 retains legacy recognition, 351 has become increasingly common among mobile and business users. Together, the two area codes serve a dynamic region balancing historical significance with modern growth.