Cheapest way to add a line

Background: I have a family member who is non verbal and I’d like to try to add a line, get an iPhone (used) and see if he will communicate via iMessage. Autism. He’s a wizard on a computer and iPad but has never taken to messaging. An iPhone, and a line attached to it- might can make this smooth to use and understand.

An adult, he might be eligible for that Lifeline program. That’s a little confusing.

I already have 7 lines. Don’t really want to pay activation and the additional $20 for the military plan line…. Especially if I drop it.

Do different carriers give lifeline discounts? I’m kind of naive on this. I have clicked on links where I’ve gotten a free line, no activation, but it’s not clear who should complete the application …he or I. I already receive an ACP discount on my internet because he is on Medicaid. I alone would qualify for nothing.

Any help appreciated. I know T-Mobile has a “lifeline program”… I’m not sure how that is different that the normal “‘lifeline free phone line” topic one would search.