For now, the movement is largely limited to small and midsize organizations and is focused around the Asterisk open-source private branch exchange and Vyatta open-source routers. Cisco and other old-time networking vendors certainly aren't yet shaking in their boots over it. But it's a growing movement that they ignore at their own peril; lower-cost, higher-function technologies have a way of replacing existing architecture far faster than vendors realize, open-source vendors say.

As you might expect, whether open-source PBXs and routers are superior to their proprietary cousins is a controversial issue. The small and midsize enterprises that have chucked their proprietary PBXs and routers for open-source systems say the new systems offer similar functionality with more flexibility and lower costs than proprietary systems. Proprietary providers, however, question whether open-source vendors offer adequate levels of support and whether those who buy them have the technical expertise needed to install and maintain the systems.

The threat to Cisco

Open-source "may not have a huge impact now, but we're starting to see some companies with 5,000 endpoints considering switching [to Asterisk]. The more that do, the more that it will have an impact," Chad Agate, co-founder and CEO of SIPBox in Tinley Park, Ill., says of Asterisk and open-source technologies. Prior to forming SIPBox, Agate had operated a company that sold Cisco systems, but he sold that firm to concentrate instead on selling Asterisk systems. SIPBox has replaced or is in the process of replacing Cisco, Nortel and Avaya systems -- some with hundreds of endpoints -- and expects more companies to follow suit.

"Open-source makes a lot of sense for nonprofits," which constitute a significant portion of SIPBox's customer base, Agate says. "They spend about 40% less than for the Cisco system and get the same feature set."