Isn't LTE band 12 the low frequency band T-mobile just purchased for better building penetration? T-mobile currently sucks for indoor reception due to it's high frequency LTE bands 
http://www.apple.com/iphone-6/specs/
http://www.apple.com/iphone-6/specs/
Model A1549 (GSM)*
Model A1522 (GSM)*
LTE (Bands 1, 2, 3, 4, 5, 7, 8, 13, 17, 18, 19, 20, 25, 26, 28, 29)
Model A1549 (CDMA)*
Model A1522 (CDMA)*
LTE (Bands 1, 2, 3, 4, 5, 7, 8, 13, 17, 18, 19, 20, 25, 26, 28, 29)
Model A1586*
Model A1524*
FDD-LTE (Bands 1, 2, 3, 4, 5, 7, 8, 13, 17, 18, 19, 20, 25, 26, 28, 29)
TD-LTE (Bands 38, 39, 40, 41)