According to his North American numbers on PBX and key systems measured by lines, open source systems account for 17.94%. He credits the open source PBX, with Nortel comes in second for 85% of those deployments or 15.24% of overall installations last year.

Nortel comes in second with behind all open source with 16.56%, Cisco comes in third with 12.53% and Avaya comes in fourth with 11%.

However, Eastern's findings are at odds with studies done by other market analysis firms that follow PBX sales. For example, Infonetics sets growth of overall PBX sales at 1% in 2008 not the 40% Eastern Management Group reports, says Mattheus Machowinski, a directing analyst for Infonetics. "We expect the market to stabilize in 2010, resume growth in 2011 and hit double-digit annual growth by 2012," he says.

He ranks Nortel, Cisco and Avaya as one, two and three for sales as measured by lines in 2008, but had open source vendor marketshare below 1%.

He seemed surprised at the Eastern results. "It's provocative; its headline grabbing," he said. "If it's really almost 20%, don't you think the PBX market [as reported by himself and other analysts] would have declined quite a bit last year?" he says. "I would have expected the PBX market to have plunged."