← Area code 231
231-871 phone numbers
Numbers 231-871-0000 to 231-871-9999 are assigned to New Cingular Wireless PCS, LLC in Beulah, MI. 4 of its ten thousand-number blocks are assigned to other carriers (number pooling).
Not assigned to any carrier: 231-871-2xxx, 231-871-4xxx, 231-871-5xxx, 231-871-7xxx — calls from these use spoofed caller IDs.
Source: North American Numbering Plan Administrator, Nov 3, 2026. Numbers can move between carriers.