what's the function of a mobile phone

Mobile Phone
Being a product of high-technology,mobile phones are being more and more widely used.It's small in size,light in weight and easy to carry,offering fast and convenient service for communication.It's of multi-function.The users use it for calling,sending short messages and internet-surfing.
In recent years,mobile phones have become popular among middle school students.Quite a few use them at school to keep in touch with their families and friends instead of writing letters,which,of course brings convenience to them.But I don't think it's good to do so.
In spite of the advantage mentioned above,student users often waste a lot of time chatting over the phone in their spare time,some even use them to cheat in exams.In addition,mobile phone bill is also a heavy burden on students' families.