This simple trick will bypass the passcode and give you access to all of the personal information on the phone including Mail, SMS, Contacts and Safari.
To duplicate this hack simply set a password on your iPhone then on the passcode lock screen follow these directions.
Step One: Tap the Emergency Call button
Step Two: Double Press the Home Button.
These steps will bring up the Favorites Menu. From here you can call your favorites or tap blue arrow next to contact's name. You now have full access to applications such as Safari, complete Contacts list, SMS, Maps, "full" Phone access, and Mail by accessing various entries on the Favorite's page, i.e. tapping their home page brings up a full, unrestricted Safari.
This security flaw makes your iPhone's password lock useless so take appropriate steps to secure your phone!