You already found the "device" answer, it includes pretty much any physical connection to the system.
I have been working the the SX-200 since the days of Generic 1001 on a single 5-1/4" floppy, there is no way to get an ONS port and the console working at the same time, however you can get the console and a Night Bell to ring at the same time to alert others so they can TAFAS the call.