@dobey I wanted to try a T-mo phone to confirm its just the CDMA versions but after a saga of talking to a lot of less-than-savvy-individuals (to put it politely), I gave up. Sold the device to a guy using it as a smart mouse-pad. I'm now using a new Note20 Ultra vanilla with the moon-shot hope of "someday."
As far as T-mo SIM cards, I never used a T-mo branded phone, but certainly did test 3-4 T-mo SIM cards. Never worked. Data was perfect. The phone would get auto assigned a temp zombie phone number during "activation" then never finish.
Interestingly enough, my old S5 which was a T-mo phone, using a Ting T-mo branded universal sim kept on working because it was activated long before the T-mo/Sprint merger. I was never a T-mo customer, only a Sprint customer with my Note4.
For giggles I tried a few cards from Ting on the Note4 as a test in comparison. It was blacklisted upstream for Ting (as they are a MVNO for both).
I don't recommend anyone trying it with anything T-mo unless the phone is branded to support VoLTE and is new (obviously not a Note4). Never-mind Note4 technically could use VoLTE (like the T-mo likely does by permission only upstream)...but it was a complete nightmare. Sad to leave this project behind...for now.