I was wondering if anyone here might have any experience with using SIM cards from different carriers in their unlocked iPhones while in the UK and Europe. I'll mostly be in the UK for the next 3 and a half months, but I'll also be doing some traveling around (probably all of the usual places: France, Germany, Amsterdam, maybe Prague and some other places). So I want something that I'll be able to use in the UK as well as some of these other countries. Having access to data (preferably 3G) is essential, since I've come to rely on it for getting around in unfamiliar places and checking e-mail, etc. Unlimited data would be preferred, but I might be able to get by on as little as 500MB per month. I'll also need to be able to place international calls without too much expense, as I'll be calling people back home in the U.S. regularly in addition to calls throughout Europe. Where I am right now (which is near where I'll be spending most of my time), my phone seems to be in the range of the carriers O2, Orange, and Vodafone. Anyone have any experience with using these carriers in the UK and Europe? Which carrier would likely be able to fulfill my needs for the cheapest while allowing me to pay for a month or so at a time?