If you recently updated your Verizon Nexus 6 to Marshmallow, you would have noticed that the VoLTE has been automatically disabled by the update. To be found under network settings, VoLTE gets you advanced calling, which is HD voice for your calls among other things.
While we can’t really force Google to correct it, we can tell you how to get it back.
Here’s how to do enable VoLTE on your Verizon Nexus 6.
Step 1. Fire up your device’s dialer. And dial *#*#4636#*#* to access hidden menu.
Step 2. Now, select ‘Phone information’.
Step 3. Next, tap on the TURN ON VOLTE PROVISIONED FLAG button. No changes would occur though, and it’s fine.
Step 4. Now tap on the TURN OFF RADIO button.
Step 5. Wait a few seconds now and let radio get turned off. Then turn the radio on after that by tapping TURN ON RADIO button.
Step 6. You’ll be able to see that TURN ON VOLTE PROVISIONED FLAG BUTTON is now changed to TURN OFF.
Step 7. That’s it. Now go to Settings > More > Cellular networks, and keep the Enhanced 4G LTE is enabled.
Big thanks goes to takaides over at Reddit, for figuring this out. Thumbs up!