As Broadband Reports reader johnnn first scooped back in December, T-Mobile has quietly been deploying their implementation of HD voice without much fanfare. Unlike upcoming versions of VoLTE, T-Mobile's implementation of HD voice doesn't eat batteries for breakfast, and it's also operating at a significantly lower bit rate (12.65kbps). As a result, calling it "HD" is probably a bit too generous, but it will mean call quality improvements for T-Mobile 4G users.

"T-Mobile has announced that HD Voice is now available on its network nationwide, dramatically improving in-call voice quality for customers with capable smartphones," said the company at CES last week.

"Customers will hear a more true-to-life voice quality that’s fuller and more natural-sounding with significantly reduced background noise from street traffic, wind and crowd noise."

To notice the improved quality, both callers must be using a 4G-enabled phone. It's less of a battery drag because it uses the current circuit-switched UMTS radio interface for the call instead of IP-based transport. Meanwhile, T-Mobile is rumored to be just days away from an LTE launch in Las Vegas, with a follow up deployment in Kansas City. VoLTE, which should offer significantly better quality that T-Mobile's HD Voice offering, has seen delays for most carriers until at least 2014.