Area code 231 – Michigan
231 has served Michigan since 1999, split from 616. 572 of its 786 number blocks are allocated (73%). No carrier dominates: AT&T 26.9%, Other CLEC / VoIP 24.5%, Frontier 9.1%. 978 FTC complaints named a 231 caller ID in the 33 days to 30 October 2026, putting it 42nd of 422 codes with five or more complaints.
- State
- Michigan
- In service since
- 1999
- Time zone
- Eastern
- Shares area with
- No overlay
Who holds 231 number blocks
Share of the 572 assigned NXX blocks (72.8% of the 786 possible), across 42 carriers. This is share of number blocks, not of subscribers.
- AT&T26.9%
- Other CLEC / VoIP21.7%
- Frontier9.1%
- Onvoy8.6%
- Verizon7.5%
- T-Mobile5.6%
- Charter4.2%
- Lumen4%
- Bandwidth3.3%
- Brightspeed3.3%
- Spok1.9%
- American Messaging1.9%
- Windstream0.9%
- Peerless0.5%
- Comcast0.3%
- Twilio0.2%
Spam complaints naming 231
FTC Do Not Call complaints where the caller ID was a 231 number, 28 Sep – 30 Oct 2026 (33 days). Caller IDs on spam calls are frequently spoofed, so these are complaints about the code, not calls proven to originate in it.
Rate centers in 231
NANPA allocates number blocks to rate centers and records their names abbreviated to ten characters, so these are NANPA's codes rather than place names – CHAMPAURBN is Champaign-Urbana, NWYRCYZN01 is a New York City zone. We show them unchanged instead of guessing at the full names. Showing the largest 5 of 99.
Timeline
- 1999 231 goes into service, split from or overlaid on 616.
More about 231
Separate pages for the questions that need their own answer: what time it is there, what the complaint data says, who holds the number blocks, and how the code compares with the one it shares its area with.
Frequently asked about 231
What state is area code 231?
Michigan.
Is a call from 231 a scam?
231 is one of the most complained-about codes in the country – 978 FTC complaints in the 33 days to 30 October 2026, 42nd of 422 ranked codes. Most of those calls are spoofed: the caller fakes a local-looking number because it gets answered more often. Look up the specific number rather than judging by the code.
Which carrier owns 231 numbers?
AT&T holds the largest share of assigned number blocks at 26.9%. The rest is spread across 3 other carriers. This is share of number blocks, not of subscribers – people keep their numbers when they switch carriers.
Do I need to dial 10 digits in 231?
No. NANPA records 231 as 7-digit dialing for local calls.
Sources and verification
- NANPA – NPA Database (npa_report.csv), file date 11/01/2026, retrieved Nov 1, 2026
- NANPA – CO Code Assignment Records, All States (utilized), file updated 11/01/2026, retrieved Nov 1, 2026
- FTC – Do Not Call Reported Calls Data, 25 daily files 28 Sep – 30 Oct 2026, retrieved Nov 1, 2026
NANPA dialing note for this code: “7D”. Reviewed by the data desk. Spotted an error? Request a correction.