Area code 866 is not assigned a geographical area, as of 2015. Area code 866 is used for toll-free numbers. Calls to toll free numbers are charged to the party receiving the call instead of the caller.
The 866 area code has been a toll-free area code since 2000. Other toll-free area codes include 800, 844, 855, 877 and 888. The North American Numbering Plan assigns toll-free and geographical area codes.
Area codes 822 and 833 have been reserved for toll free area codes, but neither is in service as of 2015. The 844 area code was put into service on Dec. 7, 2013.