Are mobile phones a necessity for school students

I personally would want my children to have a phone at school strictly for emergencies. That way my children will be able to get ahold of me. If it is just for show and my children wants to run up a bill talking and IMing their friends then no they should not have one. I think it is getting out of hand. My children don't have one, and my oldest keeps telling me that she wants one and I won't do it. First of all she is homeschooled and won't need it for an emergency. Second, if she wants to work and pay her bill, then she will have to wait until she is of legal age to get a job.