The New York Times published a piece on HD voice coming to the U.S. market via Sprint and T-Mobile.
“With HD Voice, Better Call Quality Is Coming. Text Your Friends” does a good job of capturing the painful history of cellular carriers delivering HD voice in the U.S.
The two most revealing points within the piece:
1) AT&T and Verizon wouldn’t respond to inquires on HD voice. HD Voice News is not surprised, given the problems continue to have with VoLTE.
2) An assertion by a representative of the GSM Association (GSMA) that Sprint will be able to exchange HD voice calls with other carriers because it uses the GSMA HD voice logo. This is an interesting assertion, given that there are no formal documents out of GSMA on how HD voice calls would be moved between the CDMA world (Sprint) to other network technologies (GSM and LTE).
Hopefully GSMA will provide a more detailed answer at some point rather than “If they have the HD voice logo, they should be interoperable.”