← Area code 423
423-399 phone numbers
Numbers 423-399-0000 to 423-399-9999 are assigned to Bandwidth.com CLEC, LLC (rate centre SULIVNGDNS, TN, NANPA abbreviation).
Not assigned to any carrier: 423-399-1xxx, 423-399-2xxx, 423-399-3xxx, 423-399-4xxx, 423-399-5xxx, 423-399-6xxx, 423-399-7xxx, 423-399-8xxx, 423-399-9xxx — calls from these use spoofed caller IDs.
Source: North American Numbering Plan Administrator, Nov 3, 2026. Numbers can move between carriers.