It's not a CDMA vs. GSM thing. Verizon has had transferrable SIMs for awhile. It's a Sprint provisioning thing. T-Mobile will probably just get rid of Sprint provisioning altogether by doling out TMo SIMs rather than fixing the Sprint side.
Even though the merger is well on it's way, the actual transfer from CDMA to GSM will still be a few years ? The ability to take a sim card and use it on an unlocked phone will be a big benefit vs. dealing with whitelisting of IMEI
All I know... Having this S-20 Ultra, and utilizing Tmo improved coverage in Utah (and its TONS better from like 3 yrs ago when I tried for a yr)... I cant wait to see what the combined assets will do.. Hell volte will be about as good as the standard cell coverage...
I have been hitting all the bands (except the N-bands. I think) SCP bounces all over..2, 12, 66, 71 I have had to add new notes as they are Tmo towers instead of Sprint hahahha