If the child had been told not to do it and did it make them pay the bill. Then if they keep their grades up after paying the bill then look into a plan that is unlimited. There are many things in life that are only good in small quantities and at certain times. After that I would encourage the school to limit phone time to lunch time. Passing notes back in the day would get you an hour of detention after school and a letter to your parents. If it was that easy to catch note passing then there is a dereliction of duty by these educators not to crack down on this.
Educators try to crack down on it because of the cheating angle. I know of one situation where a student got a 0 on her midterm by the school because she was caught with a cell phone in class the day of the exam.
They read her the riot act, and then asked if she wanted to tell her parents about it or if she wanted them to. Those were her choices.