Your ’s passcode entry can’t block everything, it seems — at least not with iOS 4.1 . We’re hearing various reports that simply inputting a random number in the emergency call field, pressing call, and then promptly hitting the hardware lock button will take you to the Phone app, thereby granting you access to the call history, voicemail, and address book. We’ve tried this with 3G, 3GS, and 4, all with the same result.

e830a49b9frm eng.jpg 450x258 iOS 4.1 glitch lets you bypass lock screen

See the article here:
iOS 4.1 glitch lets you bypass lock screen to access Phone app, photo album (video)