students can be in touch with their parents, and know what going on. can reach parents in the event of an emergency, and vice versa. If in danger, your children can reach family members or a close friend. Phones can be silenced during class or study periods, and active only in appropriate places. With cell phones, students can easily reach their parents for any reason: to ask them questions, change plans, or to keep in touch.
Bringing phones or tabs to school can provide an easy distraction for the students, believe you me, i have experienced it. If one boy/girl brings slowly the others follow his/her example and bring phones, and slowly almost everyone would be interested in their phones only, not in studies. Schools have phones in the principal's room for contacting parents in case of emergencies. If the principal is busy, you always have the class teacher or any teacher who is having a phone. The same can apply to change of plans. Even though the phones are silenced, there will always be children who play with it in classes. It will, inevitably stir up some kind of problem or controversy which is not needed in a school.