Well, Apple did warn customers not to unlock their iPhones, and now the firm has taken steps to prevent it happening. With the launch of the new 1.1.1 update for Apple's new gadget, users will no longer be able to use third party SIM cards, they are instead restricted to AT&T only. Although there are some reports of unlocked iPhones becoming expensive paperweights, this seems rare and no more common than it is for locked phones, with most users instead finding themselves with a 'factory-fresh' iPhone with all the stock settings restored. But to be on the safe side, if you do have an unlocked iPhone it is recommended that you either don't download the latest update or you return your phone to its locked, factory state before you update it, with all the information you need available from Engadget.