[ninjin]

A big thank you to everyone responding with information, apologies for responding only here. It looks like there is indeed still a lot for me to learn, but now I have some pointers. I have been meaning to get my hands dirty with SIP for some time, dreaming of a setup with multiple accounts and control over things like when each account allows incoming calls, etc. But, as Terry_Roll indicated, there seems to be plenty of security considerations as well which makes me somewhat uncomfortable.

Also found the /r/VOIP subreddit [1] which has plenty of reading.

[1]: https://teddit.net/r/VOIP