As it was rumored a few weeks ago, AT&T has introduced both VoLTE (Voice over LTE) and HD Voice calling. For now, both of those features are only available in specific areas of these markets, starting on May 23rd:
Of course, both of these features will continue to expand to more markets as time goes on, like with previous rollouts of new technology. For now, both of these features are limited to the Samsung Galaxy S4 Mini, but software updates and new hardware will make more devices support it.
Unfortunately, HD Voice only works if both callers have devices with HD Voice support, so unless they both currently have a Galaxy S4 Mini, users won’t get the added benefits. But now AT&T joins both Sprint and T-Mobile in having the latest voice technology. Once Verizon has HD Voice, all the major carriers will have it.