There are an estimated 55.4 million VoBB users worldwide. A better term to use would be “fixed VoIP lines” since you can have multiple users behind a business VoIP line. Out of those 55.4 million fixed VoIP lines, there are an estimated 8.1 million IP Centrex lines. The remaining 47.3 million are fixed residential VoBB lines. I have in the chart below given a market share split: market share of residential VoBB lines served by the vendor software platform.
Cisco software (the BTS platform) serves 6.8 million residential VoBB lines. That puts Cisco ahead of the others with a market share of 14.4%. Cisco's main BTS deployments include Time Warner Cable, Comcast, Cox (to a certain extent), and cable companies such as UPC in the Netherlands. Nortel is not far behind, which actually surprises me since Nortel has been focused on upgradation of existing TDM networks with packet interface. Their MCS 5200 application server that does the job in business and residential VoBB deployments has not really had much success. I am inclined to think therefore that it is the cable residential VoIP deployments of Nortel (such as the ones at Videotron, Shaw, and in Netherlands) that contribute to Nortel's rank number 2 here.
Those who might be surprised to see 'Proprietary software' having an even greater share should know that VoIP is not really as old as they think. The use of proprietary software for control, management, and feature set in VoIP offering is not new at all. I have added this post on the subject today.