I have a contract on 3 in the UK and on ATT in the US, although thinking of switching to TMo. I have always simply swapped SIMs mid-Atlantic on my iPhone 4 and I'm good to go in the other place.

I'm now looking at switching to an unlocked iPhone 5. I would get the new phone through 3 in the UK. What I have gleaned so far is that there are two different models, the A1428 for the US and the A1429 for the UK, which operate on different frequency spectrums for LTE. I have asked of 3 and of Apple as to whether, with the same phone, I can get LTE on both sides of the Atlantic (at least once 3 have rolled out their LTE network), and have had conflicting answers.

Do any of the gurus here know the answer? And does it vary whether I maintain a contract with ATT (which runs through October), or switch to TMo at that time? And am I right in thinking that 3G will be just fine in both locations?

Thank you in advance for any insights - I'm very confused!