When the
American Telephone and Telegraph Company established the first nationwide
telephone numbering plan in 1947, the state of New Mexico was designated as a single numbering plan area and was assigned
area code 505 in the group of 86
original North American area codes. On October 7, 2007, the numbering plan area was reduced in size to the high-population centers in the northwest of the state, and the rest of the state was renumbered with area code 575. The area code has been the last area code in the United States introduced by an
area code split. All new area codes added in the U.S. since have been by
overlays, in which a new code is added to an existing NPA. Prior to October 2021, area code 575 had telephone numbers assigned for the
central office code 988. 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. This area code was therefore scheduled to transition to
ten-digit dialing by October 24, 2021. ==Service area==