There are Craig stores in London from where you can find best deals on unlocked iPhone. Before buying an unlocked iPhone ensure,
* How safe was it unlocked
* Is it a permanent unlock
To avoid these hassles better you can buy a network locked iPhone for low cost and unlock it yourself. You can unlock an iPhone 4 safer and easier using remote unlocking service. You can get the remote unlocking service for an iPhone 4 from ClassicUnlocking.Com at affordable cost with easy unlocking guide. This is a permanent unlocking method and doesn't require a jailbreak too. Good luck mate.