s.joseph: vodafone cant stop you using a prepay sim if you get an iphone. There'll be some kind of global unlock right?
All Phones have an IMEI Number ( http://en.wikipedia.org/wiki/International_Mobile_Equipment_Identity ) The first 8 Digits tell Vodafone it is a IPhone 3G.
All Sim cards have a sim card number, Vodafone know weather a simcard is Prepay or not.
How can you jailbreak a phone to spoof either of these?