It will be all right if these middle school students can use their mobile phones properly.
First of all,don't use the mobile phones in class in order not to affect normal study.It is better for you to shut off your mobile phone during the class.Once any emergent things happen,it will be easy for you to call police or your family any time and any where by using your mobile phone,and if your teachers,classmates or other people need to contact someone by phone,you can also do them a favour by lending them your mobile phone.