[Freeswitch-users] how to turn an ongoing call in to a conference

Dear Support, my question for using freeswitch is: how to turn an ongoing call in to a conference so i can have the third party in without breaking up the call (no hangup, dial stuff)? something like call intrusion，A and B are already talking on the phone, then C wants to talk to both A and B. any response will be greatly appriciated. Jacob