It didn’t take long for Verizon and Apple to get their act together, and it looks like indeed Verizon using VoLTE (Voice over LTE) instead of falling back to CDMA will happen before the end of the year. The public beta of iOS 12.1.1 is out, and has enabled this.Read More
Apparently with no fanfare, AT&T has launched VoLTE (Voice-over-LTE) in Dallas, along with what they're calling HD voice. This service allows for fast data speeds while on a call, and as long as you're connected to someone also using HD voice on AT&T, you'll have a very clear connection. I happened to discover this when doing further reading from today's joint announcement this by AT&T and Verizon that they will support VoLTE interoperability between the two carriers in 2015.
Both of the photos were taken from my home office just a couple miles from the AT&T world headquarters in Downtown Dallas, TX.
More info from AT&T on HD Voice: http://landon.co/10rKqBw
More on the joint announcement from MacRumors:
UPDATE: 11:09 PM I placed my first VoLTE to VoLTE call with HD Voice on AT&T's network (The other calls were VoLTE to 4G or POTS.) and the quality is noticeably better. Definitely more along the lines of Skype or FaceTime Audio calls.