@indigomoth - Another safety precaution is to get one of those kids phones which needs a parent to enter a code before a number can be put on it, and only a programmed number can be called.
That way, you can make sure they aren't calling, say, random people they've met online, or friends that you don't want them hanging out with or something like that.
Cell phones are wonderful for emergency situations and I wouldn't want my kids to be without one, but kids aren't mature enough to know who they should be calling on their phone or giving their number to.
These days you also need to let your kids learn how to use the technology when they are young. Cell phones are used in so many aspects of our lives, including schooling. I've heard of math teachers using them in class to demonstrate problems and so forth.
You don't want your kids to be left behind, but you need to make sure they're safe as well.