Personally, the problem in schools with phones is that they are always getting stolen.
Well, for me that has never happened (I don't know if it was because I had a rubbish phone anyway!) or because kids nowadays are always showing off their new iPhone5.
Nevertheless, it is essential, especially for girls as you never know who hangs around after school also, it is important if you are staying after school, you have a detention etc. Just think about it, no phone to contact your parents, would be a pretty big hassle for them!
The other problem people have is if their phone breaks at school, well...It's the kid's fault.
Phones are simply made for contacting someone. Students shouldn't be on their phone though because their in school for a reason to learn not socialize. It's a distraction and it takes up learning time. Although students could use them during free periods and in between classes. They should not be used when class is in session.
Cell phones can cause a lot of distractions. Whether it be the kids distracting themselves, or distracting their friends, cell phones can hinder the learning environment. However, sometimes a cell phone is necessary. Important calls can be missed, important calls can be made. That is why students should be able to have their phones in their lockers. But while in class, I don't believe the phones should be on them.