Just checked the website. VoLTE is not supported at all, and there’s no aGPS, so I don’t see much of a reason to use this as a phone operating system. Maybe for just a mobile data device.

Good questions, particularly about the LTE. If you’re in the USA and not running a stock ROM, and not using a Pixel phone, there’s a good chance that VoLTE is not going to work. So you’ll have 4G data, but no voice calling.