https://www.asterisk.org/

Cool.

You still need something the bridge the IP and PSTN (telephone) worlds. That’s what Skype-out is. That’s what Vonnage is (if you strip out the crap).

• Trixbox enables even the novice user to quickly set up a voice over IP phone system. Trixbox can be configured to handle a single phone line for a home user, several lines for a small office, or several T1s for a million minute a month call center.

  • Trixbox CE — An open source solution

Supposed to support video conferencing.