I believe the generic term is VoLTE - https://en.wikipedia.org/wiki/Voice_over_LTE
EVS is supposedly transparent and full-band. http://spectrum.ieee.org/telecom/standards/full-hd-voice-wil...
Facebook audio as others have pointed out is great.
Not only that, but the codec needs to be supported at all stages of the call (the phones, the VOIP server, the trunk if external, etc), and if not it'll need to be re-encoded, which uses more CPU and reduces the call quality. As such you are probably better off just sticking with a more common, lower quality, codec. It's a chicken and the egg problem as providers won't support more codecs until hardware does and vice-versa (Twilio's SIP trunking service only supports G711, which is kind of the lowest-of-the-low).
On the other hand, calls between certain compatible LTE handsets (AT&T calls this "HD Audio" in my market) sound far better than classic landlines ever did. Ditto for good Skype calls and Facetime Audio.