I've been using an iPhone as my international phone for the better part of the last 4 years. First an unlocked, jail broken, original iPhone and for the past year a 4S bought unlocked from Apple. I've had very few problems. The two "biggest" issues I've run into are that some prepaid carriers may not offer micro SIM cards, so I have a SIM punch and the other issue is the carrier specific APN settings which unlockit.co.nz does for you.