It would be my pleasure to answer your questions. It was not made mention that the Nexus 6P supported HD Voice. I'd recommend you stay posted on sprint.com/newsroom for updates and new releases. If you have further questions or concerns, please let me know.
Sprint Social Care
Sprint S.M.A.R.T Agents Sprint S.M.A.R.T Agent are here to help Monday through Friday 6:00 AM CT - 6:00 PM CT. If you need to speak to an agent outside of these hours, please visit Sprint Chat