There is no way to solve this without losing the data. If you don't have access to the computer that was used to back it up last, it's gone. Anything that was done between the last backup and now is gone no matter what (except for anything you were syncing with MobileMe.
So far as I know, there is no way to unlock the phone using MobileMe. Once it's in this state, that's it. Personally, I'd be opening a big ole can of whupazz on my so-called "friends". Oh, and from now on, set a passcode so they can't do that.