After upgrading my Nexus 6P on Verizon to the Android 7.1.1 beta, I discovered that Visual Voicemail in the native Android dialer works! You just need to make sure that that basic (free) or premium visual voicemail is active on your line. Voicemail-to-text works too, if you add Premium Visual Voicemail to your line. Unfortunately, there is no sign of Wi-Fi calling support (yet?). HD voice has always worked on the Nexus 6P.