Seems to me OP has not heard of E-Sim
It must be a US thing as I don't understand these minor suitableness on low band and Volt or a few niche things some US carriers have but 2 phones and multiple E-Sim especially for testing seems a solution
When I lived in US we just bought unlocked phones outright
I know some users note differences in cell reception but it there really that much difference in DL speed etc that it warrants 4 purchases, when E-Sim can get you around many issues
I could care less about e sim when I have the money to do what I want but thanks

I also want to KEEP the phones that work best on each network atm meaning now and going into next fall when a new batch of phones come out when I usually buy my phones. Sorry if there was some miscommunication. I want to keep the phones I buy. That’s why I purchased the s20 ultra but ultimately it couldn’t stop me from my love of my Notes. And NO. I already own the note 20 ultra. I’ve preordered the Fold 2 and I’ll be buying 2 ‘cheap’ lol iPhone 12s on different carriers (except I’m buying two Verizon phones) lol please don’t try to bash iPhones.
I use to sell phones a while ago but these days since loopholes/plans have changed I buy to keep my phones 
best of both sizes. One on Verizon and one T-Mobile. But if not, I’ll buy two Pro Max* 