Say I get an iPhone 4 (an unlocked one from a different country, or unlock it myself if it's an option) with microSIM -- does Europe offer prepaid data/minute plans? Does it come with microSIM? I feel like SIM card is much more common. If I get iPhone 4 factory unlocked or do it myself, and if microSIM is widely available in prepaid for data and minute plans (how are these? any experience?) then I don't need to hold onto my 3GS unless I just want a backup.