Try the following code from the Asterisk CookBook:
[volume_ctrl_menu]
type=menu
*5=toggle_mute
1=increase_listening_volume
4=decrease_listening_volume
7=reset_listening_volume
3=increase_talking_volume
6=decrease_talking_volume
9=reset_talking_volume
0=dialplan_exec(conference,conference-joiner,1)
/etc/asterisk/extensions.d/conference_with_features.conf ; this is a new file
[conference]
exten => conference-entry,1,Answer()
exten => conference-entry,n,ConfBridge(9000,volume_ctrl_menu)
exten => conference-entry,n,Hangup()
exten => conference-joiner,1,NoOp()
exten => conference-joiner, n,Read(numberToDial,vm-enter-num-to-call)
exten => conference-joiner, n,Originate(SIP/{numberToDial},exten,conference,conference-entry,1)
exten => h,1, NoOp(“dialplan is in h extension”)
exten => h,n, GotoIf($[ “${CONFBRIDGE_RESULT}” : “HANGUP”]?ok)
exten => h,n, NoOp("value of CONFBRIDGE_RESULT is not HANGUP) ; or whatever you want to happen
exten => h,n, NoOp(the value is " ${CONFBRIDGE_RESULT})
exten => h,n, Goto(h,end)
exten => h,n(ok), NoOp("value of CONFBRIDGE_RESULT is HANGUP) ; or whatever you want to happen
exten => h,n(end),NoOp(“this is the end”)
