[Ben Kenobi]

There's a page on Apple's site that lists what countries it works on and the spectrum frequencies. I believe on GSM you should be fine. But one thing to keep in mind is that as LTE networks are rolled out across Europe they will be on different spectrum than is used by AT&T here in the US (which your U.S. iPhone 5 will be designed for). So you will not be able to use LTE on the phone whenever it comes to whatever country you are in. This may not matter if you are in a country that is not going to have it for a while or if you just don't care.