Area code 508 was activated for service on July 16, 1988, in an area code split of 617,[1] with a semicircle around Boston retaining 617 and the central offices in the northern, western, and southern parts of the area being reassigned to area code 508. Permissive dialing of 617 and 508 continued until January 1, 1989.
On September 1, 1997, numbering plan area 508 was split, whereby area code 978 was assigned to the northern part of the service area.
Area code 774 was added to the 508 numbering plan area on May 2, 2001, forming an overlay complex and making ten-digit dialing mandatory for all calls.
Some mobile telephone numbers assigned in the 1990s in communities in the former northern half of 508 (now the 978 area code) kept the area code after the split.[citation needed]
As of 2018, NPA 508/774 is projected to be exhausted by 2045.[2]