It's difficult to sort out PBXs from UC, says Machowinski, because many vendor sell products that cross into both areas. But to avoid double-counting revenues gleaned from products, Infonetics sorts products into buckets for PBXs, communicators and UC applications.

Microsoft's Lync server -- which the company says can replace PBXs -- is counted as a UC platform by Infonetics. Part of the reason is that the platform evolved from desktop applications, but also because in practice most Micorsoft deployments in most cases are adjuncts to PBXs, Machowinski says.

In the pure PBX market, Cisco is in the lead with Shoretel and Siemens lagging behind. Cisco jumped into PBX sales with its IP PBX and has come to dominate relatively quickly, Machowinski notes. "The incumbents say if that could happen in 10 years with Cisco, what will happen with Microsoft in the next 10 years?”

in Network World's LANs & Routers section.