Curious about International use

[silentagenda]

I know this is usually a dead-zone idea; but I'd rather be certain than not. I'm torn between waiting for the "unlocked" S4 (Nexus style), HTC One, or ATT S4. The only problem is that I'm going to be moving to the United Kingdom within the next year, and am curious if I were to get an ATT model would it work with UK networks. I'm not sure what the spectrum-ranges are in the UK, so that's why I'm asking. ATT is still using GSM-based technology (and SIM, thankfully); which makes me hopeful for this to be possible.