The United States does not have a three-digit number for international calls. To complete an international call to the United States, the country code is a single digit -- 1. To complete the call after the international code in the United States requires the correct three-digit area code.
American Samoa and Puerto Rico are both U.S. territories and have unique three-digit international calling codes. The calling code for American Samoa is 1 followed by 684. For Puerto Rico the international calling code is 1 followed by either 787 or 939 depending on the region of the island.
Canada's country code is also 1. Russia and Kazakhstan share the single-digit country code 7. Many countries have two-digit country codes, including Italy (39), Japan (81) and Mexico (52).