Mobile phone

Dear Nicholeen
My 16 yrs old son is working and going to Tafe 1 day a week on public transport an hour away. He has a mobile phone and will not put it down as he is not mature enough to manage a phone and refused to hand it back at the end of the day. However he needs a phone to be in contact with his boss and also on his Tafe days. How do I control his mobile use? Many thanks for your time.