Are you talking about flashing different firmware on the 930f or the 930t
My thought is what if 930f users can flash tmobile 930t tar and get tmobile software on a international 930f.
I mentioned this in another post because I had a att s3 that I did flash tmobile s3 firmware onto and worked great
This might get us the ability to use WiFi calling and volte.
And still be rooted since 930f it's unlocked bootloader someone can make a rom that's built off 930t source
The 930T version has SD820, the 930F has Exynos, so there's no way to make the US T-mobile firmware work on an international S7. There are also some people who have said they are going to try flashing the 930T firmware on an unlocked, SD820-based Chinese/Korean/etc. version. If this works, it should pretty much provide exactly what we would get if T-Mo unlocked the 930T, although it might prove a pain to get a hold of one of these Asian variants. Other potential bonus of this route is the possibility of getting a 64GB model.
I think what jjohn7293 is going to try to is to flash firmware from one of the European T-Mobile models (which are Exynos) onto an international Exynos S7. If all goes well, this will get VoLTE and WiFi Calling to work on the 930F on the T-Mobile US network. End result, if successful, is a rooted S7 with all the T-Mo features intact. Downsides are reputedly lesser call/data performance compared to the 820-based 930T, and any custom ROMs would be limited to stock-based TouchWiz versions. No AOSP/CM type ROMs (which doesn't matter to me, but will to a lot of people).
In either case, the odds don't look all that great, but there's a decent chance, and either (or both) could get us a satisfactory compromise to what we have now. Only time will tell.