If you're a hobbyist, a tech-savvy small business owner, or even a curious solutions engineer, what could be more fun than running your own phone system? In this post I will show you how to do just that using a $100 Raspberry Pi 4 computer connected to a Twilio Elastic SIP trunk. I'm going to use the 3CX PBX (Public Branch eXchange) software, which is easy to administer and available as a free-to-use version for small deployments.

Traditionally, a PBX has served to connect the telephone handsets in an organization with the public switched telephone network (PSTN), providing features such as an operator station, voicemail, call forwarding and so on. It would consist of a rack of equipment in a telephone closet, connected to the building wiring system, and administered by members of a technical priesthood. In contrast, this modern implementation with the Raspberry PI 4 can still work with …