I rely on phones at my school. After school I have wrestling practice and if my mom isnt there to pick me up i just send her a quick text. I hate using the phones in the office because I am shy and I find it quite awkward so that is not an option for me. Some people use their phones without permission, but I think people can have a little restraint not bringing their phones out.
Having phones at school lead to distractions. With after school activities you should use the office phone. Using a personnel phone could have legal issues with it being stolen or broken. If you are shy and find using the office phone is awkward then you need to ask a teacher to use his/her cell or room phone. It isn't embarrassing if you need it. You said that people use them without permission is just an example of how it is a distraction. If one person gets on their phone then people watch them or get on their phones and eventually no one is paying any mind to the teacher.