I have the S9+ unlocked U1 and I have flashed T-Mobile G965U firmware update with March security patch, but now I'm on May security patch. https://ibb.co/ixCnKH
Yes 100%. I bought the Samsung Galaxy S6 SM-G920I from B&H and I activated it with MetroPCS in NYC. Make sure you get the I version for 4G LTE speeds. Hopefully you found out by now, if you did not well now you can make your purchase ☺