This information window is typically left open in order to see communications from other controllers or pilots using text communication. Unread messages are shown in a highlighted colour; when clicked-on (to indicate they have been “read”) they will revert to the dimmed colour (they can be clicked again to revert to “un-read” if required).
Double-clicking on a message in the window will open a dialogue to reply to it:
The window also logs your outgoing messages, both private, COM frequency, and CPDLC. All messages, both in and out, have a time-stamp showing when they were received or sent.
Outgoing messages are originated either by highlighting another controller or observer in the respective ATC/OBS lists… or by using the Target Pop Up menu in the case of pilots.
Please note that it is not possible to send a com frequency message to somebody outside your communication range.