The days of venture capitalists throwing money at open source companies are ancient history in the high-tech business timeline. But Digium is one of the exceptions to this reality, as the open source telephony vendor recently received a nice $13.8 million boost, thanks to investors who predict bigger things for the firm.

Digium is the corporate face of the Asterisk open source IP PBX, which runs on Linux servers, as well as BSD and MacOS platforms. VC firm Matrix Partners is the company making the investment in Digium, which was founded by Asterisk creator Mark Spencer.

Asterisk is billed as a full-function IP PBX, including call control, voicemail, with support for H.323, SIP and MGCP VoIP protocols. The system can be used as a complete office IP PBX system - it supports standards-based SIP phones - or as an add-on system to traditional or legacy PBXs from such makers as Lucent, Nortel or Siemens. Asterisk supports ISDN trunking and the Q.SIG protocol for such interconnects.

Matrix Partners is not new to funding open-source companies, as it was a major investor in JBoss, the open source application server company, which was bought by Red Hat for $350 million. But it's unclear if a big buyout is in the cards for Digium. Most major IP PBX vendors also base their technology off of Linux-based systems, but include their own proprietary call processing and feature server software. Nortel itself has begun to stray from its past open-source, Linux-based roadmap for IP telephony with a major partnership announced last month with Microsoft.

Digium says it's a self-sufficient and profitable company with more than 130 partners, so maybe a buyout is not the ultimate goal for the open source firm.