Okay, holy shit, telephony is DEAD. All solutions I found were commercial, one way or another. No true system for a selfhosting heart. I will literally have to puzzle it together using an XMPP server if I want it. Holy, fucking, shit. This is baaaaaaad o_o I looked at - but not only - these: FreePBX, FreeSWITCH, Issabel, Swyx (which we currently use), Wazo and just plain Asterisk, which most of them are based off of. And good lord... None of them have any useful or good instructions - its just rah-rah about how good their solution is - but then they run on CentOS7 ... since forever. Or Debian 10 - but have their packages behind a 'Personal Access Token' (so you make an account and they see it, didnt even bother to do so, so no idea what the KYCness is). I am somewhere between sad and pissed. Like, sure... I know that regular old phones are largely dead - but THIS dead? I had no idea. o.o...
Discussion
Yeah its real bad. VOIP providers suck too IMO here in the US. voip.ms was the only company I found (out of at least a dozen I actually called (if possible) to speak with reps) that offered an affordable trunk line for a consumer and unlimited minute plans that were also affordable. With 2 DIDs and a single trunk I think I'm less than $5/month. I was also using 3CX as a pbx because it ended up being much easier than asterisk (and freepbx was pretty broken a few years ago IMO)
Look into email solutions (smtp + imap) its worse. There is basically Postfix as the MTA and Dovecot as the IMAP server and basically everything else is a set of configuration files/scripts. Stalwart mail is the only other solution I found (and am currently using)
I've had my fair fight with Postfix and Dovecot some years ago when I wanted to do email hosting myself. Well, about a decade ago. And from what you are saying, just about nothing has changed since! xD /Fantastic.../
Phone and Mail are two of the world's most essential things; but the software to use/run them is so insanely archaic, it's actually a little unbelievable.
Speaking of 3CX, I had to help a customer who somehow, accidentially, broke their 3CX instance. Turns out that they forgot to reconfigure the DNS servers on the box; so I SSH'd in and did it manually - good old /etc/resolv.conf. Haven't heared a complaint since. But while I had the chance, I absolutely crawled the whole interface and I kinda liked it.
FusionPBX isn't completely terrible - just, my ISP is. xD I have to figure out my creds' proper scheme... at some point, eventually. I'm glad the PPPoE creds they gave me actually _worked_. I have a username, password, server (whose DNS name only resolves when using their own and specific resolvers!) and something they call a VOIP PIN... But after this absolute marathon of being shocked and mentally shaken to pieces, I just haven't had the wish to sit down on it and work it out entirely. I just... couldn't.
Like, sitting there and realizing how "closed" the whole system is whilst it is actually based on technically open source software, kinda broke my heart, a bit, at least. It was... quite something.
Also with that setup I used a set of Cisco ATA for a desk phone setup to feel like a landline for work related calls at the time. I liked it and it mostly worked. The devices were not exactly compatible and had some issues, but once configured worked pretty well.