When the American Telephone and Telegraph Company (AT&T) created a universal North American telephone numbering plan for Operator Toll Dialing in 1947, Missouri was divided into two numbering plan areas (NPAs), which received the area codes 314 and 816. Area code 314 identified the eastern part of the state, from the northeast corner of the state at the Illinois border along a southwestern line near Columbia and Jefferson City to the center of the state, and continuing southeast into the east side of the West Plains area to the Arkansas state line. The largest city of the area code was St. Louis on the Mississippi river in the east.
By 1995, the telephone subscriber base experience substantial growth, threatening the exhaustion of the numbering pool.[1] Relief planning entailed the division of the numbering plan area to create a new area code, 573, for most areas outside of the St. Louis metropolitan area, which would retained area code 314. The area code split became effective at day end of January 7, 1996, with a permissive dialing period commencing until July 7, 1996, during which the new numbering plan area could be dialed with both area codes.
On May 1, 2022, the Missouri Public Service Commission (MPSC) approved an all-services distributed overlay complex for the 573 numbering plan area, effective March 24, 2024. On June 17, 2022, the NANP Administrator assigned area code 235 for the relief action, beginning with a permissive dialing period of six months on August 26, 2023 (as 573 was not affected by the 2021 requirement to change to ten-digit dialing due to the implementation of the 988 Suicide & Crisis Lifeline).[2]
