Originally Posted by Casey060492
I don't think you'll be able to use HD Voice. From what I can tell it requires the 1700 mhz band, which hd voice works off of on tmobile and the AT&T version of the G2 is lacking that band.
That's not the case. T-Mobile's HD Voice (or AMR-WB) is simply another codec that's supported in the radio. Even though it's bitrate is fairly modest, T-Mobile only supports it when the user is on HSPA/HSPA+ -- regardless of its RF band used (ie: no EDGE/GPRS, despite that it would technically work).
Now -- whether something needs to be tweaked to get the radio to cough up the codec -- that I don't know. I do know that unbranded, non AWS (pre T-Mobile) iPhone 5's support HD Voice without any modification, so there isn't anything proprietary that T-Mobile needs to do to a handset to provide support.
Interestingly, a T-Mobile branded G2 will clearly display a yellow "HD-Voice" icon in the upper left corner of the display while in a call. To the OP -- have you called another known T-Mobile user that has an HD Voice handset, while you're both on the T-Mobile network and both on (at least) 3G?
also, don't use a Bluetooth headset while trying HD Voice out. You need an HFP 1.6 headset to get HD Voice via BT. While the handset will still negotiate AMR-WB properly, older BT headsets munge the bandwidth to the point that it sounds like a non-HD call.