Locked iPhone, don't know the password?

I have an iPhone 4s through AT&T and the other day one of my friends decided it would be cool to set a password on my phone and not tell me what it was. It was just meant to be a joke but they don't remember what the password was so now my phone is locked and I can't access anything because I don't know the password. What do I do!

Sadly, you have to plug it into iTunes and do a restore on the iphone. You could maybe back up the device first but everything on the ipod will be deleted when you do this restore. But its the only way to by pass the lock screen.