Will a US iphone 4 be able to work in the uk?

So my uncle who lives in the usa has agreed to give me his iphone 4 coz of his upgrade to the 5. The problem is that its locked to te a&t network. If he gets it unlocked do you think taht i can use it in the uk? With a uk network? With a uk simcard? He says it Supports gsm 850, 900, 1800 & 1900

Yes, once unlocked it an AT&T 3G phone will work internationally
The ATT system is basically the same (unlike teh t-mo US 3G/GSM system)

I would look at getting the (UK) t-mobile "iPhone" PAYG sim
- they do a Free 12 months data for iPhones

http://www.t-mobile.co.uk/.../sim-only/
"For a limited time, you can also get 12 months free internet with an iPhone microSIM."

If he gets it unlocked, which costs about $5 on eBay or FREE through AT&T, then you should be able to use it in the UK only if you have a service that uses SIM Cards.

For example, Verizon and Sprint both use CDMA networks and do not use SIM cards.AT&T does since it is GSM. Hopefully your service in the UK uses SIM CARDS. Make sure your uncle is able to unlock is completely, and make sure he tests it out with T-Mobile before sending it to you.

Edit:
Also make sure you can get a hold of a Micro SIM. They are probably free if you ask from your carrier in the UK or you can buy a tool to cut your original sim!