Flight Intercom can be accessed by the Control Column trigger (Bottom of the switch) or the PTT on the ASP in the I/C position.
Flight Intercom is both pilots and the Ground if plugged into the flight inter phone position.
Service Interphone you need to select on the ASP and use the Mic switch on the control column trigger. (Top of the switch) or the ASP PTT in the Mic position.
Service Interphone is the Cabin crew or if on the ground with the Service Interphone Switch on a number of external ground positions.