International Mobile Termination Charge (IMTC) is an additional per minute charge that is applied to all international calls originating in the United States and terminating in certain countries to (1) wireless devices; and (2) ranges of fixed or wireless telephone numbers which the foreign telecommunications company designates to be for special services. Because many foreign telecommunications companies impose extra fees on AT&T to complete these calls, AT&T charges the IMTC, in addition to all other applicable charges. The IMTC charge amount varies by country and changes from time to time. Be sure to check codes and rates periodically for current information.
A complete chart outlining countries and rates is available from this link.