AWS also has a GSM network. They are moving from the American TDMA standard to GSM, hence have two parallel wireless networks. You can see this reflected in their rate plans - they offer "TDMA" plans and "Next Generation" plans.

Be aware that not all GSM phones can be used in Europe. The U.S. uses different frequencies for cellular - 800MHz and 1900MHz, vs 900MHz and 1800MHz in Europe. There are lots of GSM phones which support only the North American frequencies.

I don't find unlocked phones to be all that important. For one thing, it's possible to get any given phone unlocked - just check Ebay. As well, when signing a service contract, the carrier will heavily subsidize a new phone so you get it free, or at minimal cost. So the ability to use your old phone on a new network doesn't seem that valuable to me.

My $.02

- JimY