Regular Meet-me VDNs are limited up to 6 participants, even in CM 4 (I administer one of these and tried to set it up). To get more (up to 300 participants) you need a dedicated S8500B server, known as Expanded Meet-me Conferencing (
http://www.avaya.com/gcm/master-usa/...nferencing.htm), which connects to the CM via SIP. It requires CM 3.0 or higher.