US -> UK iPhone Activation Strategy

[synoxis]

I intend to purchase an iPhone in New York when I visit next week. I will be thinking of buying both used and new iPhones.
Could someone help me research the models that I should buy in order to be able to use the iPhone in the UK, the models that are unlockable, I really wish to avoid the situation where I have an expensive brick. Any other advice pertinent to the situation will be greatly appreciated.

Thanks in advance,

synoxis.

[ianbroste]

If you look on craigslist.com there are usually quite a few jailbroken/unlocked iPhones on there