Approved all the way back in the year 2000 by the Missouri Public Service Commission, NPA 557 was initially scheduled to enter service towards the end of 2001, providing relief for NPA 314, serving the city of Saint Louis, Missouri and a number of towns and cities to the west and south west including Florissant, Creve Coeur, Kirkwood, Sappington or Oakville.
The activation of the new area code was later postponed indefinitely, while 10 digit dialing was in the meantime introduced for a number of area codes in October this year.
In August 2021 a new date was agreed upon for the introduction of new area code 557. This new date is August 12, 2022. The dialing plan for the new Numbering Plan Area overlay complex 314/557 will be as follows: 10 digits for local calls and 1+10 digits for toll calls.
See official planning letter with detailed map of new overlay complex 314/557 (PDF document).