My only addition to Roland1975's post would be that you can setup either of the two Stations that are termination points for the other stations auto-icom button, to autoanswer for icom.
That way the recieving end of the call, beeps and out answers to the speaker phone, when the originator press their Intercom button.
This way the phone doesn't have to be manually answered to complete the call. (like the intercom boxes from the 'old days')
Have Fun !
Cam