Yeah that makes no sense because only this year's non-CDMA model supports 700mhz band 30 which is where all T-mobile's expanded coverage is coming from. No way is that poster correct.
Edit: my bad it's band 12. Maybe he's right.
Band 12 is 700Mhz, which every 6S model supports. Band 30 is AT&Ts
Model A1633* (iPhone 6S GSM)
Model A1634* (iPhone 6S Plus GSM)
LTE (Bands 1, 2, 3, 4, 5, 7, 8, 12, 13, 17, 18, 19, 20, 25, 26, 27, 28, 29, 30)
TD-LTE (Bands 38, 39, 40, 41)
TD-SCDMA 1900 (F), 2000 (A)
UMTS/HSPA+/DC-HSDPA (850, 900, 1700/2100, 1900, 2100 MHz)
GSM/EDGE (850, 900, 1800, 1900 MHz)
Model A1688* (iPhone 6S CDMA)
Model A1687* (iPhone 6S Plus CDMA)
LTE (Bands 1, 2, 3, 4, 5, 7, 8, 12, 13, 17, 18, 19, 20, 25, 26, 27, 28, 29)
TD-LTE (Bands 38, 39, 40, 41)
TD-SCDMA 1900 (F), 2000 (A)
CDMA EV-DO Rev. A (800, 1700/2100, 1900, 2100 MHz)
UMTS/HSPA+/DC-HSDPA (850, 900, 1700/2100, 1900, 2100 MHz)
GSM/EDGE (850, 900, 1800, 1900 MHz)
Models sold by whom confirmed through:
http://www.pcmag.com/article2/0,2817,2491013,00.asp
With the iPhone 6s, AT&T confirmed that it's selling the model (A1633/34) with its new Band 30, which will speed up AT&T LTE service across much of the country. But that model doesn't appear to have a CDMA radio, which is needed to make calls on the Sprint and Verizon 2G/3G networks.
All the other carriers are selling model A1687/88, an Apple retail rep told me. T-Mobile confirmed it is selling the 1687/88, as well. That includes support for all four carriers, including the LTE bands AT&T has installed until now, just not the brand-new Band 30. So A1687/88 will work fine on AT&T, but in the future it may get somewhat slower LTE speeds on that network than A1633/34.
That's strange. I bought a T-Mobile 6 last year and it works fine on Verizon including LTE.
So I did some research, and it depends on where you get it from. If you got it from either T-Mobile or from an Apple Store bundled with a T-Mobile SIM, then it's T-Mobile hardware. As in, you get LTE from CDMA networks like Verizon, but not 2G/3G. If you got it unlocked and full price from an Apple Store, the policy is to actually give you the full Unlocked version of the phone, regardless of which carrier you're on, which would have the CDMA hardware (in the 6's case, the Unlocked phone that they started selling around January of 2015 is just the Sprint phone without a Sprint SIM. Same bands and everything)