To initiate a multipoint call using an IP/VC 3540 or 3510 MCU, the endpoint dials the appropriateservice prefix followed by a conference ID. (The conference ID can be up to 9 digits long.) If a service on an MCU is 40880 for a 384-kbps call, the user might dial 4088011223, the call would be routed to the MCU using the 40880 service prefix, and the MCU would initiate an ad hoc conference with an ID of 4088011223. Users can also initiate a call and invite the other participants by dialing the conference
ID, the invite string **, and the E.164 address of the another participant.
http://cisco.com/application/pdf/en/us/guest/netsol/ns280/c649/ccmigration_09186a00800d67f6.pdf