I dual-SIM my iPhone 15 ProMax to allow for carrier diversity - Verizon (native, non-MVNO) is primary, USMobile as secondary. Recently swapped over to their “Dark Star”/AT&T access and it’s been a huge improvement over T-Mobile. If it wasn’t for my Verizon plan being a fairly decent deal (along with providing peace of mind for the wife, which is worth every penny), I’d consider going that route as my sole carrier. T-Mobile unfortunately can’t win that title for me, because they are severely lacking in network resiliency, at least here in the Houston metro. Their cell sites lack power redundancy (generator), causing service to be hard down after approximately 30 minutes into one of our occasional long power outages.