About a mobile phone.

Actually, it was my homework and I decided to place this text to check if everything is ok with grammar.
I remember the time when mobiles were the symbol of prosperity because only very wealthy people could afford to possess them. Now times have changed and almost everybody has a mobile phone. But is it a great invention? I think it has both advantages and disadvantages.
The first and main advantage is that you have a phone on hand wherever the network exists. It makes people free and confident. For example, one can make a call to police, ambulance service or fire brigade as fast as possible. That is very valuable, particularly where there is no wired phone.
The second advantage of a mobile phone is that you don't need to memorise a lot of phone numbers. Every mobile has storage for phone numbers.
The third advantage of a mobile phone is that you can see who is calling you and then you have a choice to answer them or not.
There are also some disadvantages of mobiles.
Firstly, mobiles could cause road accidents because they could divert attention of drivers.
Secondly, mobiles could cause addiction. I think a lot of people can't escape the desire to talk on a mobile every moment when they have free time.
Thirdly, I think one disadvantage of mobile phones is that a lot of young people are passionate about text messages. It may substitute real communication.
In conclusion, I'd say, despite of all disadvantages, a mobile phone is a really amazing thing.