1．手机使用的普遍性；
2．手机的优点；
3．手机的危害及我的建议。

[写作导航]

     先指出当前手机使用很普遍，然后用事实(随处可见人们用手机通话，许多中学生，甚至小学生都有手机)来支持主题句；手机的优点主要是方便通信，甚至上网，还体现在突发事件(疾病、交通事故)的求助上；手机的缺点主要是辐射和干扰他人，因此我建议尽量少用，重要场合(开会、上课时)关机。

参考范文

      Mobile phones have become more and more popular in China these days. Wherever you go, you can see people using mobile phones. Many high school students, even primary school students, have mobile phones.

      Mobile phones have brought people a lot of benefits, but the most important is that they are convenient. With mobile phones, they can keep in touch with anybody they want. If they want to get some information from the Internet, they can easily have their dream realized through mobile phones too. Furthermore, if someone has a heart attack or a traffic accident, an emergency call to hospital or to the police can quickly bring him help he wants.

      However, mobile phones can also bring people problems. The most serious is the electric wave radiation which is thought to be harmful to users' brains. Another problem is that when people are having a meeting or a class, the ring of the mobile phone may interrupt others. So I think people should use mobile phones as little as possible and turn them off when they are attending an important meeting or a class.