I recently bought a Iphone 3gs from a person online, and little did I know it has a demo software on it!
When the phone is set to lock in 1 minute, after that 1 minute the demo video shows, and also you cannot change this screen saver, add a password to your iphone, or add/remove/move icons/apps.

How do I get this phone out of demo mode? Iphone is version 3.0

Thanks

You can restore it on itunes and it should be fixed