In the Cisco CallManager 4.x, the maximum number of participants default value is set to four. In order to change this, complete these steps:
Choose CCMAdmin Webpage.
Choose Service > Service Parameters. Choose the Server and choose Cisco CallManager as the Service. Choose Advanced.
Do a search for Maximum Ad Hoc Conference, which is located under the clusterwide parameters (service). This parameter specifies the maximum number of participants that can be in a single Ad Hoc Conference.
Also, the number of participants allowed depends on other factors as well. Refer to the Multipoint Conferencing section of IP Video Telephony for more information.