It doesn't matter what u do as long as you hook your phone to Odin and flash uvuemk2 you'll then be literally Tmobile branded and On theyre STOCK firmware only ties you have to Metro is your subscribed to there service .
That's when u look for the 379mb kit kat ota.
That will be downloaded it allows you to do this cause it sees your on stock Tmobile firmware
pulling data from tmobile towers
M919n= gsm = tmobile.
We use tmobile data
We're just metro subscribers.