Best solution is to tweet Legere about it. That guy is a rock star that always looks out for his customers!
Just an FYI... It was Google's issue for not supporting 3xCA on T-Mobile. They have a fixed radio/baseband in the Android O DP3 which, once flashed to the radio partition of stock and other N firmwares, works with T-Mobile. I did this myself by extracting the file from the O DP3 factory image and fastboot flashing it.