← Area code 815
815-558 phone numbers
Numbers 815-558-0000 to 815-558-9999 are assigned to United States Cellular in Rockford, IL. 6 of its ten thousand-number blocks are assigned to other carriers (number pooling).
Not assigned to any carrier: 815-558-2xxx, 815-558-3xxx, 815-558-5xxx, 815-558-8xxx — calls from these use spoofed caller IDs.
Source: North American Numbering Plan Administrator, Nov 3, 2026. Numbers can move between carriers.