Area Code 231

You can increase your connection rate up to 30% by dialing from a local number.

Local Presence by Tenfold gives you one-click access from your existing phone system to a local number in the US area code 231 and more than 200 others.

Reach out to customers in Muskegon, Traverse City, Big Rapids, Cadillac, and Cheboygan.

Source: Wikipedia