Others see open-source as a trend that could impact Cisco's business, though perhaps only with IP PBX units. Vyatta provides an open-source router product but is much newer in the market, so it's too early to determine its potential impact, analysts say.

Vyatta's free Open Flexible Router, like Asterisk, runs on off-the-shelf software. Yet Vyatta offers the same WAN routing and security features as the proprietary technologies.

Even Sam Houston University, which is converting to Asterisk, is maintaining its Cisco routers and not switching to an open-source router system, says Aaron Daniel, the institution's senior voice analyst (http://www.computerworld.com/action/article.do?command=viewArticleBasic&articleId=9003272) .

"We're replacing Cisco [IP PBX] with Asterisk because it's more cost-effective," Daniel says. "With Cisco, we have to pay a license fee with each additional phone. With Asterisk, we don't have the license and our technical team can make any changes that we need."

But the open-source infrastructure offerings aren't as good right now as the more traditional systems, he believes, so "we will remain a Cisco shop" in terms of infrastructure," Daniel says. "Open-source [routing] solutions tend to be slower."