Jeremiah Grossman said..
iPhone is a quad-band GSM phone and will work around the world. Before you travel, make sure that international dialing and roaming are enabled through AT&T and that the places you’re going offer GSM coverage. International roaming rates apply for any voice or data usage outside the domestic coverage area. Substantial charges may be incurred if you take your phone out of the U.S. even if no services are intentionally used.