← Area code 231
231-391 phone numbers
Numbers 231-391-0000 to 231-391-9999 are assigned to Bandwidth.com CLEC, LLC (rate centre WALLOON LK, MI, NANPA abbreviation). 3 of its ten thousand-number blocks are assigned to other carriers (number pooling).
Not assigned to any carrier: 231-391-1xxx, 231-391-2xxx, 231-391-3xxx, 231-391-4xxx, 231-391-5xxx, 231-391-6xxx — calls from these use spoofed caller IDs.
Source: North American Numbering Plan Administrator, Nov 3, 2026. Numbers can move between carriers.