Unanswered: AT&T Mobile for UK?

Hi,

If I buy an american mobile and unlock it, will I be able to use it in the UK?

I've seen a HTC that I really really want..
but it's not made for the UK.
However, the website says it is unlocked.
Will I be able to use it on a Three sim card?

I did want the HTC HD Mini, but discovered that it isn't Android.
:/

Thanks.