May be time to jump ship. On Sprint, it works for both M8 and Harmon Kardon Edition. On Verizon, it works on M8 for Windows, too.
And for Sprint, the HK Edition is only $129.00 for eligible upgrade from the HTC site.
HTC EVO Upgrade to HTC One (M8) | HTC United States
And for Sprint, the HK Edition is only $129.00 for eligible upgrade from the HTC site.
HTC EVO Upgrade to HTC One (M8) | HTC United States