I'm kinda with tehiota and gfunkdave on this. It sounds like a fun project to tinker with. I'm the kind of person that spent high school configuring Windows domains and running my own Exchange server, and running things like FTP servers on my first Android phone. But for something like this, if it's something I need to rely on for "production" use, I'm happy to pay the $0.85/month to VoIP.ms. If nothing else, it's way cheaper than the electricity for the box I'd have to run.