If you're smart, you don't put him on your plan at all! If he has wacked out his credit, chances are he'll have little concern for yours. If he runs up a big overage bill you are responsible to the carrier regardless of any agreement between the two of you. If he "recently finished his contract" means he has a carrier that he should stick with, because regardless of his credit rating as long as he stays current on what he owes them, they're not going to disconnect him. Also, for those with bad credit there are a lot of pay as you go plans such as the "GO PHONE" or "CRICKET" that he can get. If you believe it a possibility that you may have to enforce an agreement in court, it isn't very wise to enter into that agreement in the first place.