The 866 area code does not serve a specific geographic region. The area code 866 is used for toll-free numbers, specifically those in North American Numbering Plan countries.
The North American Numbering Plan consists of twenty-five countries and territories in North America and the Caribbean. This design requires that all telephone numbers include a three-digit area code, a three-digit central office code, and a four-digit station number. The area code 866 is comparable to other toll-free number prefixes, including 800, 844, and 888. Calls to these prefixes, including the 866 area code, are free of charge, as the expense is borne by the owner of the telephone number.