When I was a child I was fascinated with rotary phones. I still have few of them, so I decided to connect them in one home-made telephone network. I found broken analog PBX on internet auction. Firstly I wanted to restore it and use its original parts. But on the other hand introducing to it some modern technology would be like more fun for me. With RaspberryPi you can build everything, also VoIP PBX.
Still working on this!