Thanks to Linux and a security flaw in the iPhone OS you can now get into your phone if you forgot your passcode. This happens on non-jailbroken phones as well.

The security flaw was found by security and IT blogger Bernd Marienfeldt. Here is how he was able to gain access.

Basically, he said, plugging an up-to-date, non jail-broken, PIN-protected iPhone (powered off) into a computer running Ubuntu Lucid Lynx will allow the people to see practically all of the user's data — including music, photos, videos, podcasts, voice recordings, Google safe browsing databases, and game contents.
This same trick could lead to a buffer overflow that would allow full read/write access to the phone. The phone tested was a 3GS running various firmwares. And tested on jailbroken devices and non jailbroken devices. It worked for all the phones tested.


Source: iPhone security flaw: Using a PIN won't help - Security- msnbc.com