Skip to content
AI Dialer

Michigan · United States

Area code 231: where it is and who calls from it

  • ET (UTC−5/−4)

Reviewed by Sujan ThapaliyaLast updated

What is area code 231?

Area code 231 serves Michigan, United States. It is in the ET (UTC−5/−4) time zone.
Where area code 231 sits in a North American number: the three-digit area code, then the three-digit exchange code, then the four-digit line number, all under country code 1. The diagram also shows the two validity rules — an area code never starts with 0 or 1, and a repeated middle digit marks a service code such as 800 for toll-free rather than a place.
The 1 you dial before a ten-digit number is a long-distance prefix, not part of the number itself.

Area code 231

Type
Geographic area code
State / province
Michigan
Country
United States
Time zone
ET (UTC−5/−4)
In service since
1999

Step by step

How to call a 231 number

The same ten digits, dialled three different ways depending on where you are calling from.

  1. 1

    Within the same area code

    Many carriers still allow seven digits inside 231, but overlays have made ten-digit dialling the safe default. Dial 231 followed by the seven-digit number.
  2. 2

    From elsewhere in the US or Canada

    Dial 1, then 231, then the seven-digit number — eleven digits in total. The leading 1 is the North American long-distance prefix, not part of the number.
  3. 3

    From outside North America

    Dial your country's exit code, then 1 for the North American Numbering Plan, then 231, then the seven-digit number. On a mobile, type + instead of the exit code: +1 231 followed by the number works from any country.

Background

About 231

231 still permits seven-digit dialling for local calls, which is now unusual — most of North America moved to ten digits as overlays were introduced. It has no overlay, so the code alone still identifies the area, and that is what keeps the shorter dialling plan workable. It entered service in 1999, carved out as the numbering plan was expanded to keep up with demand for numbers.

Unwanted calls

Why you are getting 231 calls

The reason an unfamiliar 231 number keeps calling is usually neighbour spoofing: automated systems fake a caller ID in the recipient’s own area code because a local-looking number is answered far more often than an unfamiliar one. The number displayed is frequently not the number placing the call, and may belong to someone with no idea it is being used.

What actually helps:

  • Let unknown numbers go to voicemail. Automated diallers rarely leave a message; a real caller will.
  • Do not press any key to be removed. On an automated call, a keypress confirms a live human and increases the volume you get.
  • Register on the national Do Not Call list and report unwanted calls. It does not stop fraud, but it does constrain legitimate telemarketers.
  • Turn on your carrier’s call-filtering service. Filtering now uses STIR/SHAKEN attestation, which is why properly signed business calls get through and spoofed ones increasingly do not.

If it is your 231 business number being labelled as spam, the cause is different and fixable: unregistered caller ID name, low attestation, or a volume pattern carriers read as automated. Owning your numbers, registering CNAM and signing at Attestation A is what resolves it.

If you are calling into 231 rather than receiving from it, the relevant reading is branded caller ID — the same signals that decide whether a call from this code gets answered decide whether yours does.

Frequently asked questions

Where is area code 231?
Area code 231 covers Michigan, United States.
Is a call from 231 a scam?
Not inherently. 231 is a legitimate area code serving real people and businesses in Michigan. But spam callers frequently spoof caller ID to display a number in your own area code, a technique called neighbour spoofing. If you do not recognise the number, let it go to voicemail; a genuine caller will leave a message.
What time zone is 231 in?
231 is in the ET (UTC−5/−4) time zone. Check the local time before calling back so you are inside normal business hours.
Can I get a 231 phone number?
Yes. Local numbers in 231 can be provisioned in minutes and used for calls, texts, and as your outbound caller ID. A number in the area code you are calling is answered noticeably more often than an out-of-state one.

Sources

  1. North American Numbering Plan Administrator — NANPAArea code assignments, relief planning, and which codes are in service across the North American Numbering Plan.
  2. ITU-T Recommendation E.164 — The international public telecommunication numbering plan — International Telecommunication UnionThe international number format, the 15-digit maximum, and how country codes and national numbers compose.

Get a 231 number for your business

A local 231 number, owned by you, with your business name on the caller ID and callbacks routed straight to your team. People answer local numbers, and they answer branded ones far more often still.

  • Branded caller ID (CNAM)
  • STIR/SHAKEN Attestation A
  • No subscription
Get early accessBrowse numbers