See also:

Conference Call
When two calls are in progress (one active and one on hold), press and hold the button until you hear a double beep indicating that the two calls have been joined into one conference call. ...

Listening To Audio With The Screen Closed
To listen to only audio portion of the channel with the screen closed: • Set the audio to the desired source and channel. • Close the video screen. • To change the current audio mode, press ...

Join Calls
When two calls are in progress (one active and one on hold), touch the “Join Calls” soft-key on the Phone main screen to combine all calls into a Conference Call. ...