I would also like to the know the answer to this as well. As far as I have been told the phone should hypothetically support all U.S. bands being used from a hardware standpoint atleast.
band 2 / 1900 MHz PCS (Americas)
band 4 / 1700 MHz AWS (Americas)
band 5 / 850 MHz Cellular (Americas, Oceania, Brazil, Israel)
band 12 / 700 MHz Lower 700 (USA (AT&T, T-Mobile, regional))
band 13 / 750 MHz Upper 700 (USA (Verizon))
band 17 / 700 MHz Lower 700 (USA (AT&T))
band 25 / 1900 MHz PCS+G (USA (Sprint))
band 26 / 850 MHz Extended Cellular (USA (Sprint))
band 29 / 700 MHz Lower 700 (USA (AT&T))
band 30 / 2300 MHz WCS (Americas (AT&T))
band 41 / 2500 MHz BRS / EBS (USA (Sprint))
band 66 / 1700 MHz AWS-3 (Americas)
Yes it does but to unlock all the bands can end up frying your radio and even reducing battery life. There's ways to do it and can be found in developer places.
I would definitely agree with @tidbits but also add that Neville Ray (TMO CTO) has been quite public about how TMO worked with Samsung to take advantage of all of TMO's network enhancements (QAM 256, 4X4 MIMO &CA) some of which only TMO has implemented to achieve near GB LTE (in the lab of course) by being able to utilize all of them together. You never know how Samsung has the different bands programmed in the radio to work with Bands the radio might support versus those that they have active in just the -T model.
I haven't seen anything public yet about which Bands the SM-G950/955T have in it compared to the other versions of the phone.
Here you go straight from Samsung themselves.
2G GSM: GSM850,GSM900,DCS1800,PCS1900
3G UMTS: B1(2100),B2(1900),B4(AWS),B5(850)
3G TD-SCDMA: B34(2010),B39(1880)
4G FDD LTE: B1(2100),B2(1900),B3(1800),B4(AWS),B5(850),B7(2600),B8(900),B12(700),B13(700),B18(800),B19(800),B20(800),B25(1900),B26(800),B66(AWS-3)
4G TDD LTE: B38(2600),B39(1900),B40(2300),B41(2500)
This is perfect you my friend are a god send.
Will the T-Mobile version work on Verizon?
TL:DR Yes and no
Yes if you flash Verizon firmware
No if you don't flash Verizon firmware
Flashing becomes the TL:DR and complicated to explain.
Any news you can give me on how or where to do this?
Currently there is no way to do this as of yet. You can check XDA and see if anything pops up.