If i buy an iPhone in America will i be able to use it here in the UK?

Since its cheaper to get a phone in america, if i buy one that is unlocked and bring it back home with me. Will i be able to use it here? If i took it to a phone shop such as Orange for them to put an orange sim in it and use it here etc?

Yes, the american iphones have the required bands so it will work. I know you will at least be able to run 3G, EDGE, and GPRS. However stuff like siri doesn't work cause when i was in england on o2 with an american iphone she would reply "i'm sorry can't search names in the uk".

I'm not sure if it is changed, but it didn't work when I bought iPhone4 in US and used here.