My ol'lady has a carrier that uses Verizon towers.
But when we travel, I always bring my AT&T phone for 'just in case'.
When my wife and daughter decide to go on road trips they usually head to, California, utah, or Arizona and their T-Mobile service works fine.
Last month we went for a road trip to northern Nevada and she kept losing coverage with t mobile ( I connected her and the daughter to my Verizon hot spot) we also brought a long my Google Fi phone.
Eventually we got back into TMobile coverage.
So with Verizon, T-Mobile and Google Fi we are pretty much covered anywhere we go
It actually saved our rear ends when we were in southern Indiana and there was no Verizon coverage at all.
I had Sprint, and now T-Mobile, and neither of those work there either.
Only my AT&T would work.
We go there every year (The Boogie), so we need SOMETHING that works in case we have an issue.