Gizmodo today reported about an easy way to access the Address Book, Mail, and Safari even if you turned on the Passcode Lock.
The trick is quite clever — press the "Emergency Call" button and then double-tap on the Home button to show the list of favorites in the Address Book. Through the address book record it is possible to launch Mail or Safari, without entering the Passcode.
It is just one of many reasons to use a program like 1Password to make sure the sensitive information on your iPhone is encrypted.