iPhone 4S prices start from £399.00 @ smartfonestore - refurbs - All networks available at time of posting.
if you have this amount to spend up front , just buy a sim only plan to go along with it giff gaff is reasonably good and no contract needed!
60 Day Warranty
Boxed with USB Cable
ALTHOUGH it says 60 days warranty the 4S has only been released for a few months so you should still have the remainder of warranty i.e 8 months or 9 months etc.
I have purchased an iPhone 4 from here and it came in mint condition as new.
Unlocking wise orange , t-mobile handsets are very easy to unlock at a cost of £20-£25 of ebay. This is an official unlock done through apple servers.
I have seen members also mentioning that vodafone is easy to unlock.