Are mobile phones a useful tool?

I think mobile phones are very useful because you can use it them for whatever you want, whenever you want and wherever you want, for example if you need to sign something up or search for something on the internet simply by giving a button you already have everything and you can save all the information you need and not lose it, because if you write it down on a paper it is possible that later you will lose the paper or you don´t remember where you wrote it down.

I also think there is are some disadvantages because not all people have enough money to buy a good mobile and they are also very fragile and can be broken or lost to a minimum.