Area code 406 is the telephone area code in the North American Numbering Plan for the entire U.S. state of Montana. It has been Montana's only area code since the American Telephone and Telegraph Company created a nationwide telephone numbering plan in 1947.
As of 2013, there were 1.7 million lines served by 47 carriers; all but two wireline providers support local number portability (the exceptions are small rural independents Hot Springs Telephone Company and Northern Telephone Cooperative). Sufficient available codes for new exchanges in the 406 area code exist to meet anticipated demand until 2031; number pooling has been implemented in response to increased demand and inefficient use of 406 numbering resources.[1][2]
Prior to October 2021, area code 406 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.[3]
^Inbody, Kristen (27 Nov 2017). "In Montana, it's 406 exclusively until 2031". Great Falls Tribune. www.greatfallstribune.com. Retrieved 13 June 2023.
^"Montana PSC Granted Authority to Implement Mandatory Number Pooling". fcc.gov. 12 December 2015. Archived from the original on 10 December 2017. Retrieved 7 May 2018.
^"Transition to 10-digit dialing (for 988 as 3-digit access to National Suicide Prevention Hotline)" (PDF). North American Numbering Plan Administrator. January 8, 2021. Retrieved March 9, 2021.
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