I have been there, too! My DD 14 spent $100 one month on texting and an accidental $350 the next month, by having the AIM (IM) set up. I was so mad at her! At the time we were looking at getting new phones and adding unlimited text. Needless to say, we did not get new phone or unlimited texting. We didn't think it sent the right message!
You have gotten great advice today!! I love the idea of having the kids do housework to pay their bill...since they are to young for a job. I am going to talk to my DH about this.
PS- This thread made a great dinner discussion this evening.