The numbering plan area was designated in 1947, when the American Telephone and Telegraph Company (AT&T) devised a comprehensive telephone numbering plan for the United States and Canada.
In 2020, 988 was designated nationwide as a dialing code for the National Suicide Prevention Lifeline, which created a conflict for exchanges that permit seven-digit dialing.
Area code 605 was therefore scheduled to transition to ten-digit dialing by October 24, 2021.
[1] Current projections suggest that South Dakota will require a second area code by late 2026, as the existing 605 area code is nearing exhaustion.
[2] The numbering plan area includes the following communities, which are serviced by the listed central office prefixes.