I was previously with Sprint, which then eventually went over to T-Mobile. While on Sprint, I got 3 free promo lines. One of the devices on that free promo line wasn't supported any longer and I got an email that I would qualify to get a free phone on the line since it wasn't supported. So I was like, yeah let's do it and then after I got it, they started charging me for it. Tried to get it reversed but the damage was done and I couldn't get a free line back on it, which makes sense as it was in the terms which I neglected to fully read.

I got another free line from T-Mobile so now I'm back to 3 free lines, which is cool because we wanted the 3 lines. 

Now, we have the 2 paid lines with the phones we want, one on an EIP from Samsung and the other paid off. The 3 other lines have hand me downs from us but recently, one of the phones is failing and I need to get a new one and we aren't upgrading the 2 paid lines anytime soon. 

As shown, 2 are the 2020 line on us from Sprint and one is the recent one from T-Mobile. 

Now, I understand that they don't qualify for promotions and I shouldn't involve them in anything that would give me a discount since it would lose the free line discount but what I want to know is if I purchase a phone for one of those 3 lines through and EIP, no discount, full price, will that terminate my free line promotion and start billing me for it? 

Has anyone done an EIP through one of the free lines? Any suggestions on how I can proceed to ensure I don't lose my free lines. 

Purchasing a device on a free line from Sprint or T-Mobile through an EIP via Apple or T-Mobile