I wrote something myself because I wanted PGP support, but saw some apps on Google Play (I've been still using it back then). I can't recommend anything, sorry.
For calls - yeah, tough stuff. I'e been looking to do the same thing you did, and found there are GSM USB dongles (modems) that can work with Asterisk to forward calls, so you'd use a raspberry pi instead of a smartphone. But I never implemented it, people gradually stopped calling me and there was just no motivation.
Which hypervisor? I tried booting a physical install this year with VirtualBox and two decades ago with VMWare Player and both times ended up with damaged bootloader that was unable to boot from bare metal