I typically find cellphones to be huge distractors in the classroom.  If the teaching methodology is lecture, then I would argue that cellphones stay in the car and for emergencies students can be reached via calling in to the front desk.

However, a better approach may be to utilize cellphones in the classroom.  If there are opportunities to use them for learning and set times to have them put away and turned off, there may be better compliance.  I would argue that for most assessments structured as a series of questions to answer that cell phones need to be off… >>>