The most advantage of having a mobile phone is you can communicate to your family and your friends no matter what where you are. For instance, you can contact easily to your friends by calling or sending messages everywhere without electricity. It is maybe the main reason why almost all people today choose to own a mobile phone. 
> Reduce the word count by deleting the repetition of the same idea.
> You have used all these words to point out that mobile phones are mobile.
Using a lot mobile phone can harm your brain, particularly teenager and children who are under 16 years old. 
> using mobile phones a lot can harm your brain
> spell out the number 16 as a word
Using mobile phones is said to be harmful to the brain, especially for those who are under the age of sixteen.

If you use mobile phones too much, you will get bad effects like dizzy, blood-brain barrier, or ears problems. 
> Blood-brain barrier is not a harmful effect. It is a part of the body.