Sometimes you have to just let them learn.  It seems to be the case that when a parent is too strict with exposure to the world then the day they turn 18 they go off the deep end.  I have a good friend still recovering from drug addiction from a situation like that.

A gradual exposure is best I think.

But out of curiosity, what exactly are you worried your 16 year old is going to do with a phone that you see as a problem?