I started Fusion because I was a broke software developer who couldn’t afford a phone system, so I decided to build one myself. I was 19 and learning PHP on the fly. It was a thoroughly inappropriate language for a phone system, but it was the one I knew. That was enough to get me started.
The software is a PHP Back-to-Back User Agent (B2BUA), using the PHP Threads library to handle the involved SIP protocol in a high-level language.
The software takes a class-based approach to receiving and dispatching incoming SIP messages on a public port. If anyone would like to use a PHP user agent in their software, please get in touch!
