lNomNoml:
Sounds like theft to me, the money should be returned if it is not used. It's understandable about the can't keep the connection active for ever argument but that does not entitle the provider to just keep the money if it wasn't actually used.
Why not? It's exactly how prepay works on every single network everywhere in the world.
At the end of the day there is still a cost to a network of maintaining an active user.