i would test it first but it is likely that they have
to phone out of the network as certainly in the UK all the carriers run a blackbook system where if a phone is lost or stolen and you report it to them they will lock it and black list it meaning it wont be able to make calls on any network in that country - as far as i know the system hasnt been moved worldwide so selling it in another country might work.
FYI i am working of knowledge i picked up about 4 or 5 years ago when i had several phones stolen from me