HD voice has been a promise of mobile carriers for quite a while, and it is finally becoming a reality. So far, only T-Mobile has been able to provide nationwide HD voice to users in the U.S. even though Apple touted it as a feature of the iPhone 5 back in 2012. Sprint also offers HD voice (though it isn't available to iPhone users). Verizon has said that HD voice is on the way in 2014, and now AT&T has also confirmed that this will be the year for HD voice.
Of course, you may remember that AT&T promised in April of last year that HD voice would be coming before the end of 2013, and that obviously never happened. Today at CES, AT&T Mobility CEO Ralph de La Vega said once again that the company will launch HD voice services at some point this year. He said that the newly announced Padfone X would be the first device to support HD voice on AT&T's network. We're hoping that he meant the Padfone X would be the first new device released to support HD voice, because there are plenty of existing devices that we would hope to be compatible.
No word on when HD voice will be coming, but if the Padfone X is planned as the flagship device for the service, we would expect that HD voice would be coming at the same time as voice over LTE (VoLTE) and LTE-Advanced, both of which are said to be supported by the Padfone X.
source: AT&T via The Verge