make sure you go with him to alter his plan accordingly. when i got my own modem and told them to drop the monthly fee, they ditched my unlimited plan for another one that basically kept me paying the same amount. if he can afford it, its almost worth it to keep the Xfinity modem because when it acts up you can just go swap it out for a new one and be up and running pretty quickly. after years of helping older folks with tech issues, ive found this is really the easiest.