From the FCC website
"On October 25, 1996, the FCC released a Report and Order in WT Docket No. 96-82 (text) eliminating the individual licensing requirement for all aircraft, including scheduled air carriers, air taxis and general aviation aircraft operating domestically. This means that you do not need a license to operate a two-way VHF radio, radar, or emergency locator transmitter (ELT) aboard aircraft operating domestically. All other aircraft radio stations must be licensed by the FCC either individually or by fleet.
Aircraft operating domestically do not land in a foreign country or communicate via radio with foreign ground stations. Flying in international or foreign airspace is permitted, so long as the previous conditions are met. If you travel to a foreign destination, however, (e.g., Canada, Mexico, Bahamas, British Virgin Islands) a license is required. "
TJ