Nearly three years since Jon "maddog" Hall predicted that "VOIP using an open source solution, such as Asterisk, will generate more business than the entire Linux marketplace today," open source VOIP for the enterprise remains a wild frontier. SMB uptake has been considerable, as open source VOIP's promise of control and cost savings make it a natural fit. But when it comes to large-scale implementations, open source voice has yet to get most enterprises to listen.

That's not to say that the enterprise is deaf to the benefits of open source itself. To be sure, companies are increasingly vetting open source alternatives before considering commercial wares. But despite this interest in open source elsewhere in the enterprise, the phone system has, by and large, remained off-limits to open source experimentation.

When it comes to open-sourcing dial tone, the feeling among most enterprises is that there's just too much at stake. After all, network troubles translate to help desk calls and lost revenue, but if the phones go down, it could mean life or death. And when it comes to melding the lockstep world of traditional five-nines PBXes into the land of Patch Tuesday and the frequent reboot, calling on a commercial vendor can feel a lot more comforting than signing off on that level of responsibility yourself.

That said, the notion of an all-out VOIP implementation -- ripping and replacing to the core -- is fast fading away. Yes, dial tone has crossed the network boundary, but not pervasively. Moreover, many traditional PBX vendors are backing into the VOIP market, allowing telephony admins the comfort of tried-and-true PBXes with some of the benefits of VOIP. Introducing VOIP modules that permit VOIP trunks between locations is becoming common, yielding long-distance cost reductions without disrupting the status quo for local voice.

Largely, VOIP is becoming a PBX replacement on an as-needed basis. And such targeted installations could prove a sweet spot for open source VOIP. As the technology gathers steam, convincing enterprises of its efficacy in increments, it will most certainly join the pack of large-scale go-to VOIP candidates down the line. After all, the considerable cost savings and flexibility of open source VOIP are just too great to ignore.