After buying TWO i phones and having to get a refund on both due to being locked or stolen please be warned its not as easy as it seems .
Firstly if the i phone is locked to another NETWORK other than the one your on you might have trouble . You could get someone to jailbreak it eg use a program to reset it to the network you want . But this does not always work and might muck up the software ! If you do take it to a shop please ask how they are going to unlock it . The cost might be over £100 to do it for you .
Second the i phone might be lost or stolen please don't think this is an easy matter to get round because its not . All i phones have built in tracking so if your found with one you might spending a time with the Police to explain yourself .
The best way forward is going to a main supplier and getting a reconditioned one for peace of mind !
you have been warned