You can text more than one person at a time to get a mass message to them, instead of having to call each person individually.
Cell phones can hold contacts and their information, like numerous phone numbers, address, emails, etc. You can edit contacts on a cell phone with greater simplicity than you can in an address book.
They can store pictures and videos that you may not exactly need but could use later. It comes in handy when you dont have a camera on your person.
Most new phones have navigators and directions like global posititioning systems,etc.
Cell phones can hold music too.
You can call people when necessary, for instance when you are not at home and do not have access to a land-line telephone or the electricity is out, or your telephone is not properly functioning.
There are notepads on cell phones so if there is something important that you need to write down and use for later, then it can be typed in the notepad and saved. This comes in handy if you do not have a notebook, piece of paper, or a writing utensil with you. The notebook space is limited to the space on a memory card or hard drive, which can easily fit all of the text you could fit into a conventional paper notebook. Conventional notebooks are limited to the amount of pages they contain.