AT&T's Voice Over LTE (VoLTE) network is expanding and now has reach over more than 295 million Americans across the United States, as AT&T reports. With VoLTE, AT&T's 'talk and surf the Web at the same time' rule applies to 4G LTE data in addition to other forms of data.
But the big news that AT&T really wanted to share is that they're rolling out cross-carrier support for VoLTE that would allow AT&T customers to enjoy the same HD voice with subscribers of other carriers where VoLTE is supported. At this point in time, the feature is incredibly limited to certain customers in the United States, and AT&T is testing the feature out with certain carriers before it continues to expand.
Originally Posted by AT&T
With VoLTE, customers can enjoy a richer conversation that sounds more like you're talking to a person and not a muffled telephone. The voice quality is hugely improved over the traditional standard quality telephone call all thanks to extended frequency ranges of audio signals.