T-Mobile bought Sprint specifically for band 41. It's what they're using to launch 5G / NR, since T-Mobile didn't have the spectrum for a real deployment. Sprint was using most of it between LTE and NR, which was why they had to shut down Sprint NR to re-purpose that spectrum for T-Mobile NR. In many markets Sprint (now T-Mobile) has about 160 Mhz of band 41.
They've also started consolidating LTE in band 41. Sprint was pretty.... loose with allocations. For example, femtos used 20 Mhz at the bottom of the band, then their small cells used 20-40 Mhz right above that. The middle sat unused (except 40 Mhz allocated to NR in some markets), then macros had 3 20 Mhz carriers near the top. Within the past week, they shifted the macros to the very top of the band, and moved the small cells to use the same earfcn as the femtos, freeing up another 20-40Mhz and making the middle section more open. They're deploying NR in the middle. Some markets reverse this, with macros at the bottom and femtos/small cells at the top, but the middle was basically always unused (licensing reasons). T-Mobile initially launched with a 40 Mhz N41 carrier, but it has expanded to 60 Mhz in many places. NR allows up to 100 Mhz carriers, whereas LTE maxed out at 20 Mhz.
By the way, N41 is also TDD, since the band is unpaired in the US (it's paired spectrum as band 7 in Canada and other parts of the world). The nice thing about NR is that the timing configs can be dynamic, so the upload:download ratio can change dynamically depending on demand. For LTE, an entire region had to be on the same timing configs or the network would basically have massive interference. Sprint kept the whole country on the same timing configs. They originally launched with config 1, and then later moved to config 2, which allocated a higher percentage of the time slots to download than upload compared to config 1 http://www.techplayon.com/expl....