We actually pay for all our kids' phone service because T-Mo let us add them for $10/month each line. If they raise it 5 per line it will add quite a bit but I think I'd just ask the kids to pay their $15 a month then, or spin them off if they prefer, and save money overall, T-Mobile has already saved us thousands of dollars over the years, improving service without raising the price so they have a little bit of loyalty from me. It may get shitty from now but it's been a good run for 15 years at least.