I have a friend who will be travelling to Europe this fall. she will be in england for a few days, then Greece, then she will be in Copenhagen, and finally italy. She has with her an unlocked iphone 3GS. What would you advice her best options are for prepaid cell phone company in terms of international roaming? Is there any single company that could cover her for most of northern Europe,? Please drop the link of a website which provides the relevant info.