Seems that a tip has been discovered lately but we can label this under security hole flaw that must be addressed. A brazilian guy posted on Vimeo that if you dial a certain combination of pound signs from your iPhone 4 lock with passkey screen you can have access to your phone app, therefore see al your contacts.
On your iPhone with the screen asking for your passkey (See image below) you will have to:
- Tap Emergency Call
- Then enter a non-emergency number such as ###
- Next tap the call button and immediately hit the lock button
- It should open up the Phone app where you can see all your contacts, call any number, etc.
This could clearly be classifies as a security hole because if you loose your iPhone anybody can access your phone (contacts and place calls) data and it could bring you serious problems. below is a video from the Braziian guy showing how he does it.