iPhone Xs and up if B71 is a concern, if your area has B12 then anything back to the 6s. Samsung S6 and newer are compatible with B12, and anything S8 and newer is able to be swapped to T-Mobile firmware via a software update. S9 and newer for B71. Everything back to the OG Pixel for B12, and Pixel 3 for B71.
I don’t know what everyone is talking about with VoLTE being bad. In my experience calls are clearer than my ATT VoLTE. Also first root scores came out today and guess what? They used a S9 last year with calling plus and Sprints calling scores tanked. Now they are using the S10 5G for Sprint and the Note 10+ 5G for the other three carriers and Sprint calling score have skyrocketed across the board using VoLTE. One test jumped from 75(calling plus) to 95(VoLTE). Sent from my iPhone using Tapatalk