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.
For that one time when systemd-logind crashed on every boot on an unmodified CentOS install because of an OOM.