Area codes that were not already using ten digit dialing and where the central office code 988 was already in use (i.e. there exist phone numbers in the area co

Area codes that were not already using ten digit dialing and where the central office code 988 was already in use (i.e. there exist phone numbers in the area code of the form 988-NNNN) were required to switch to ten digit dialing for this (or renumber the 988-NNNN numbers, which is what area code 701 in North Dakota did).