I do have a Sprint Sim card in place.
For those in question about needing a new Tmobile sim card for their 5g, don’t do it. You will still get 5g on their towers using Sprint branded sim cards that are still being issued with these new 5g phones.
The caveat to having the Sprint sim vs the Tmobile one is: The Sprint sim you can pick up either Sprint or TMobile towers while on the road. Using just a TMobile sim card, you will lose the ability to jump on different towers while traveling, thus you may lose service in between. The TMobile sim will only pick up their tower and not link to any Sprint tower.
5g capability is fine using the supplied Sprint sim card and their tech department told me to hold on to mine vs trying the TMobile out. Your phone will pull from a 5g type tower first before the Sprint towers, as in my case at my home. My coverage was said to get better in the next month or so as we found a 5g antenna less than 500 feet away from my home that was about to be activated in a city park. Who knew, right? 😉
This is where you choose your battle on best coverage if you travel like myself and want more towers in your favor vs a dead zone… To me having the choice of two cellular carrier towers vs one brand was a no brainer…:-)