A user on a MacRumors message forum let everyone know that anyone can trick the iPhone passcode locking by simply tapping "Emergency Call" on the password-entry screen, then double-tapping the Home button, that will afterwards lead the intruder straight to the “victim’s” iPhone's Favorites, a list of frequently called contacts and their details. If any of the contacts have email addresses or websites associated with them, the trick also allows access to the iPhone's email application and Safari browser, at the same time.

Apple is aware of the problem and is preparing a software update to fix it although the exact date is not known yet.

The vulnerability has been known for some time, as far back as the first generation iPhone. "The Passcode Lock feature is designed to prevent applications from being launched unless the correct pass code is entered," said Apple's advisory. "An implementation issue in the handling of emergency calls allows users with physical access to an iPhone to launch an application without the pass code. This update addresses the issue through an improved check on the state of the Pass code Lock."

Here is what the Apple support forum recommends users to do in the meantime: "[Set] the iPhone so that double-clicking the home button will take the user directly to the home screen, which if password protection is turned on, will eventually lock the screen."

The iPhone 3G has gone on sale in about 22 countries since its launch July 11.