How do I use a showroom model of an iPhone 4S? A friend of mine bought an iPhone 4S. It was a showroom model and it came with his limitations. You can't delete or move around apps. What does he need to do to get rid of this demo-modus. Or is it irreversible? 

EDIT:
He bought the iPhone in Belgium (so, it has no sim lock)
I would suggest doing a DFU restore. You can do this by:


Plug your iPhone into a computer running the latest version of iTunes.
Hold the home button and the sleep/wake button for exactly 8 seconds.
After this 8 seconds is up, release the sleep/wake button, but continue to hold the home button until iTunes recognizes your iPhone.
Then, choose the Restore option (this should be the only option) and wait for iTunes to download the necessary software and restore your iPhone.