Although BR enforces the "No cellphones except in the piazza or in the cafeteria on your lunch time" I don't believe it is possible to prohibit cellphone use at school. Approximately 99% of students have a cellphone, or electronic device carried on them almost at all times. To completely ban cellphones in the age of electronics even sounds absolutely Ludacris. The rule is put in place to set a guideline to follow instead of a rule, since everyone already disregards it. There would be outrage and chaos if the school were to put in metal detectors and other security screening in order to prevent them being brought into the school, from not just students, but parents as well.
However, in the classroom, I believe it should be the teachers discretion whether or not they want to allow cellphones. Essentially, students are supposed to be in school to learn, and by allowing them to have their phone you are providing a distraction to the lesson. If students absolutely need to make a call arrangements can be made to make a call in the office so cellphones are unnecessary. Cellphones also provide the opportunity for cheating, theft, or even cyber bullying at school.
On the other hand, with cellphones in class students have the internet as a resource, cutting down homework time. Even if a student wants to waste the time on their cellphone during class time it is there responsibility to complete the homework/assignment at home. It is their fault if they fall behind and start failing the course.