After subtracting those OS PBXs that are not used as the day-to-day telephone system for company employees—and these non-production systems clearly remain the majority of today's Open Source PBX downloads--we conclude that in 2008, 2.86 million Open Source PBX end points were installed. Nortel, the largest manufacturer of conventional business telephone systems, lagged Open Source by 8%, having sold 2.63 million lines. (Despite Nortel's recent problems, their historic strength across all market segments has allowed them to keep the lead, at least up to this point, in our reckoning of the vendors' cumulative market shares.) Cisco and Avaya followed at 1.99 and 1.75 million lines respectively.

The total market was 15.88 million lines, giving Open Source PBXs an 18% share. That places Open Source ahead of every PBX/key system manufacturer (see Figure 1).

Figure 1: IP-PBX Market Shares

Looked at another way, were there no Open Source PBX, then the traditional PBX and key system market might have been larger by the same 18%, reflecting substantial vibrancy.

Companies using Open Source PBXs cannot be pigeonholed. Apart from technology businesses one expects might be users, we found high concentrations of OS PBX systems in many vertical markets, specifically Finance, Education, Government, Health Care, Manufacturing (non-technology), Retail, and Transportation. Of all 22 industries studied, constituting the universe of North American businesses, we observed to varying degrees Open Source PBXs in each of them. Almost 40% of companies with OS PBXs have no connection to the technology industry.

The size of a company does not bear on whether it uses an Open Source PBX to handle business communications. Hundreds of companies we surveyed have more than 1,000 employees. Dozens have more than 20,000. Two thirds of businesses with Open Source PBXs have multiple locations, though not necessarily with an Open Source PBX at each site. This means if companies using an Open Source PBX are pleased with the experience, there is a lot of runway for implementing additional systems at other locations. The study found 68% have two or more business locations, 13% have at least 11, and 3% percent have more than 100 (see Figure 2)

Figure 2: Total locations of companies with open source PBX

More than half the study companies had more than one Open Source PBX, and it was not uncommon to find five systems or more installed within the enterprise.