My son has trouble accepting responsibility for things. I thought that having a mobile with a monthly contract would help him with that... unfortunately, there have been some teething problems

.
However...
He has now been to the phone shop and knows how to check his balance.
I have set him a daily limit, which he checks throughout each day so that he stays within the limits.
I have put together a check sheet so I can keep tabs on what he is using on a daily basis (using my account with the phone company).
He is still extremely sorry for what happens and understands that now all of his responsibilities are laid out in front of him, he will be recieving some sort of DEATH if he doesn't adhere to them.
We have made it clear to him that as a result of his actions, we have had to make sacrifices (not goats or anything like that... just restrictions on our usual lifestyle) and he will be paying a percentage of the bill .
I really need him to accept this responsibility and learn some limits. He has no excuse now. He has his limits set.
I am using this as a life lesson for him. I have expressly refused to change the tariff because he needs to learn (one way or another) because in a couple of years, he aims to be an officer in the RAF and if I don't teach him some responsibility, he'll be like a chicken in a pirhanna pool when he goes through the training process.
I am hoping that the severity of his actions will help to cement the responsibility in his mind.
(No weird web-sites or downloads were in his bill... I checked all 300+ pages... just chat to his girlfriends and mates from school).