The long road to nationwide HD Voice coverage has begun for AT&T. So long as you live in select areas of Illinois, Indiana, or Minnesota. And have a Samsung Galaxy S4 Mini. Yeah, they're starting small with this one. HD Voice is a hot buzzword for carriers these days, but so far their implementations have all varied in ways that have proven to be limited and incompatible.
AT&T's first public testing here is admittedly very limited. HD Voice really only makes a difference when both callers are using compatible phones (which so far has meant compatible carriers too). When they are, both get much clearer and richer voice transmissions thanks to the increased bandwidth that HD Voice offers. Just imagine, hold music that doesn't sound like crap.
That said, AT&T's initial testing here is a small target market and we'd be surprised if many of those involved meet the prerequisites of having a Galaxy S4 Mini that they're using to call somebody else on AT&T with a Galaxy S4 Mini in the test areas. But if they do, crystal clear voice calls may await.