Even if your phone is protected with a passcode, experts found a security glitch on the iPhone
4 operating system 4.1 that lets a snoop access your call records, voicemail, look through the phonebook, and even make calls without the any knowledge of the passcode.
If you’re still using an older iOS on your iPhone 4 such 4.0, you may want to wait on that upgrade until the security glitch is fixed. All it takes to bypass the passcode security is by tapping the “Emergency call” button, then entering three pound signs, hitting the green call button and immediately pressing the lock button. This will open the phone as if there was no passcode at all.
If you decide to try it on your own iPhone you might have trouble exiting the phone app and will need to dial a number first to be able to return the phone back to normal. Testers also tried this hack on the older iOS 4.0, which proved to be secure from the glitch.
As of yet, Apple hasn’t released a response to this glitch but we assume that there will be an updated, glitch-free iOS coming to iTunes very soon.