Rather than me trying to explain it, here’s the description given by their web site:
Get virtual phone numbers, and build business apps with the easy drag ‘n drop editor. OpenVBX comes with applets for auto-attendants, call forwarding, voicemails (with transcription), receiving text messages and more.
Integrate OpenVBX with your existing systems. Build your own custom phone applets with just a little bit of PHP. Rebrand and resell OpenVBX to your customers.
Give every user their own phone number and personal conference line. Dial whole departments, share voicemail messages with the team. OpenVBX is for companies and collaboration.
It comes from Twilio, which is a cloud-based communications service. OpenVBX is an open-source project which was started by Twilio. You host it on your own server – Twilio has not announced any plan to host a version. If you don’t want to host it in your home/business then you can easily find a paid host that offers one-click installation of OpenVBX (just like installing WordPress on your blog).
There are a few apps available on their website and you can write any that you want and easily add it to your installation. You’ll need to know some PHP, but that’s a pretty common language in today’s world, so if you don’t know it then it’s easy to find a programmer who does.
I found a great tutorial for a basic installation over on MakeUseOf which will get you started. I’ve bookmarked it and put this project on my to-do list. It sounds like a great weekend project, especially with the cold, snowy weather on the horizon.