Definition of International callback:
Automated dialtone-providing setup that allows the residents of other countries to enjoy the US long distance charges (the lowest in the world) for international calls. Typically, a foreign subscriber (1) dials the phone number of a US-based callback service provider and hangs up after it rings, (2) immediately receives a call from the service providers computer which gives a dialtone, (3) proceeds to make international calls, and hangs up when finished. The US provider is paid via a credit card or a prepayment arrangement.
Meaning of International callback & International callback Definition