USA to UK iPhone compatibility?

I was wondering if anybody had bought an iPhone in America to use in the UK,
If I buy an unlocked iPhone it should work right?
Also I have a blackberry now so will I need to call my provider to change internet packages?
I already know I will have to get my sim card cut to a micro sim,
Any help would be appreciated

As long as it is unlocked, you should be fine.
Internet setting should automatically be set once you insert another sim card.

The problem is not whether or not it would work… You'll be able to make calls and do texts… It's what kind of data connection you would have.

Look at the frequency listings on this page:

Note that the GSM frequencies for 3G and 4G networks are different between the UK and the US.AT&T markets the only American GSM-based iPhone, and they use different frequencies than the ones in the UK.So, at best, you would get a 2G/EDGE data connection, which is very, very slow.

Based on the cost of the phone, even a used one, you would be wasting your money. Your American iPhone would be a very expensive brick that makes calls and texts.