According to a recent Engadget post, AT&T set to beat Verizon by deploying high-definition calls over LTE this month:
“With so many apps, services and features on today’s smartphones, it’s easy to forget that there are still plenty of people out there who still actually make calls. Eager to leverage the speed and efficiency of existing LTE networks, providers like AT&T and Verizon are busily trying to enhance voice call quality with a technology called Voice over LTE (VoLTE). Given the vast delays in deploying the service — both carriers wanted to launch it in 2013 — it’s apparent that VoLTE has presented its fair share of technical difficulties. AT&T, however, is now ready to flip the switch in select markets: sources familiar with the matter have indicated that the carrier plans to beat Verizon to the punch by rolling out VoLTE beginning on May 23rd.”
I find it interesting that carriers are positioning VoLTE as a technology that increases voice call quality.