It looks like the iPhone lock screen provides just a marginal level of protection. [Jordand321] discovered a key combination that opens the contact app on a locked iPhone. Just tap the emergency call button, enter the pound sign three times (###), then tap call and immediately tap the lock key on the top of the phone. If this is confusing just look at the video after the break to see how it’s done.
You don’t get access to everything on the device. But this does give an attacker access to all of your contact data and allows that person to make any calls they desire.