406
Area code
MT
United States geographic area code, in service since 1947-01-01.
Statusin service
Introduced1947-01-01
JurisdictionMT, US
Local dialing10D
Time zoneMountain
Last verified2026-09-17
Utilization 97% of assignable prefixes assigned
As of 09/17/2026
0%768 of ~792 assignable NXX values (200–999 excl. N11)100%
Prefix-level assignment does not equal number-level exhaustion; thousands-block pooling extends capacity. First assignment on record 2001-04-18, most recent 2026-06-05.
Area codes serve rate-center geographies, not municipal boundaries. “MT” identifies the jurisdiction, not an exact city footprint.
Top assignees
Ranked by assigned prefixes · initial assignee ≠ current carrier| Rank | Assignee | Prefixes | Share |
|---|---|---|---|
| 01 | QWEST CORPORATION | 132 | 17.2% |
| 02 | CELLCO PARTNERSHIP DBA VERIZON WIRELESS - MT | 119 | 15.5% |
| 03 | NEW CINGULAR WIRELESS PCS, LLC | 74 | 9.6% |
| 04 | ONVOY, LLC - MT | 43 | 5.6% |
| 05 | TRIANGLE TEL. COOP. ASSN., INC. | 39 | 5.1% |
| 06 | NEMONT TEL COOP INC | 33 | 4.3% |
| 07 | MID-RIVERS TEL. COOP., INC. | 27 | 3.5% |
| 08 | LEVEL 3 COMMUNICATIONS, LLC - MT | 27 | 3.5% |
| 09 | CHARTER IP ENABLED SERVICES, LLC | 26 | 3.4% |
| 10 | 3 RIVERS TEL. COOP., INC. | 26 | 3.4% |
Important: these are initial assignees from NANPA CO-code records — the carrier a prefix was originally assigned to. Because of number portability, the current serving carrier of any individual number may differ.
Change history
Recorded events for this NPA- 1947-01-01Area code 406 entered service.
Planning letters & orders
Primary documents| Date | Document | Subject |
|---|---|---|
| 2021-01-08 | PL-556 ↗ | Transition to 10-digit dialing (for 988 as 3-digit access to National Suicide Prevention Lifeline) – supersedes PL-544 |
| 2020-08-17 | PL-544 ↗ | Transition to 10-digit dialing (for 988 as 3-digit access to National Suicide Prevention Hotline |