Iphone 3GS could be broken into using a simple but effective trick but this has now been fixed with a firmware update.
Before you could this with the following steps; when the password was enabled you just press the emergency call button and then double tap the home button twice. This takes you to whatever shortcut you assigned to the iPhone home button. If this is iPhone favourite as person trying to get in would have been able can access the personal details of your Favorite contacts and call them; if it's the iPod, they can listen to your music (which isn't as big a problem).
It was a tiny problem, but a problem all the same and one that Apple fixed fast.
Before, all you had to do was choose emergency calls, tap the home button twice and then you would be in the iPhone. Fortunately, this is no longer the case as as anyone who connected their iPhone to their laptop for an update would have closed off this loophole.