Ken,
I don't think so....given....the phones don't ring if they are in use - just "notifies"....
....setup translation of the 3 ext. #'s to the same # - setup 3 shared lines - example: 2001, 2002, 2003 - do a FB (forward busy) on 2001 to 2002, and 2002 to 2003.... All calls are initially directed to 2001 - which if not busy will ring both phones...second call comes in - and it will try 2001 - which is a shared and busy line, so forwards to 2002 - which WILL ring on the SECOND phone (the one that is not handling 2001) - however, when the 3rd call comes in - neither phone will "ring" - only a "ring notice" in the headset/handset....
If you put a third phone in the loop and shared line 2002 - it will ring....but not the two in use....
John