There are 1,000 three-digit numbers, if you include every combination from 000 through 999. In North America, though, 3-digit area codes have significant restrictions. The
… first digit cannot be 0 or 1 and the second digit cannot be 9. Area codes of the form N11 are not allowed due to conflicts with short codes for things like emergency services (911) and TDD relay (711). Other area codes with the second and third digits the same (such as 800, 888, 844, and 900) are reserved as "easily remembered" codes. That brings the total down to 648 regular area codes plus 64 special "easily remembered" codes. Two of the potential regular area codes are in use for non-geographic purposes (area code 456 for international inbound 56K data communications, and area code 710 for special use by the U.S. federal government), and some of the "regular" codes will be assigned in the future for non-geographic use either as toll-free codes (after 800, 888, 877, 866, 855, 844, 833, and 822 are exhausted) or as PCS numbers (after 500, 533, 544, 566, 577, 588, and 522 are exhausted). As of August 2014, there are 300 geographic codes in use in the United States, plus 6 in U.S. territories, 36 in Canada, and 20 in other countries and territories. There are 15 non-geographic codes in use throughout the NANP, plus one just for Canada. (MORE) 
