The iPhone 5/5S both have band 17 to support at&t's 700Mhz lower B/C blocks. T-Mobile is currently deploying 700Mhz A block for their own LTE network. Band 17 is a sub set (B/C) of the superset band 12 (A/B/C). My question is, can apple push a baseband update or software update of some sort and allow iPhone 5/5s to support band 12? If no, is it a hardware thing that prevents the phone from being able to support band 12?