Sure, let him access a computer about which no one of the staff has any clue about freely. Add an UMTS USB dongle and you have the perfect communications gateway for all inmates. I am not saying that they don't have the off phone stashed away anyway, but let's not make things too easy
I do basically agree that it is always better to give inmates something to do, preferably something they enjoy and can use in the real world once they are out. But I am not convinced this specific idea is good.
"I say we take off; nuke the site from orbit. It's the only way to be sure." - Corporal Hicks, in "Aliens"