For my personal thought ,cell phones are the good way easily to contact everyone .
If you get on the bus, and it breaks down or something else happens, you have an easy way to call your parents. Same if it never shows up at school. (YES, our bus drivers have a cell phone, but it is extremely hard to get them when the something else happens as people who don't have their own fight for it. This is the main reason why my parents completely disagree with the cell phone policy, there has been several times where my dad had to track me down and was pretty unhappy about it.)
If a family emergency happens someone can text you to let you know what is going on.
If after school activities are cancelled you can call your parents.
Chanokporn 043 3EN