[2] All telephone numbers in Mexico have ten digits, of which the first identifies one of the eight principal geographic regions of the country.

[3] As of 2020, the dialing procedure for mobile phones in Mexico no longer requires the inclusion of the number '1' after the country code.

New area codes were assigned in the overlay format to address number exhaustion: in 2017, Toluca and Puebla and in 2018, León, Mexico City, and Tijuana.

In the early development of International Direct Distance Dialing (IDDD), Mexico elected to join World Zone 5, instead of joining the North American Numbering Plan (NANP).

Use of the area codes was formally discontinued on February 1, 1991, requiring callers to use international dialing.