Business phone service — RingCentral and the like — runs $20–35 per seat per month, locks your desk phones to their firmware, and puts your dial tone at the mercy of someone else’s cloud. I replaced all of it with a self-hosted PBX that costs a few dollars a month in actual usage, keeps every phone on hardware I own, and adds something the commercial offerings either charge extra for or simply don’t do: push-to-talk intercom between rooms. Dial the kitchen, it answers itself on speaker, you talk.

The whole thing is four Docker containers on one host, one DNS record on another, and a single SIP trunk in the cloud. Everything else is a text file.

A note on the examples: this runs on my real network with real family phone numbers on it. Every phone number, personal name, and account identifier below is synthetic — invented for illustration and drawn from the 555-01xx range reserved for fiction. The configuration is real and copied verbatim from the running system; only the personal data is swapped. If you build one of these, keep your own credentials and family numbers out of your blog. I’m practicing what I preach.