In-Flight Messages
There's not a whole lot to this, you have a message string limited to 64 characters, a short note string similar to the TIE95 FlightGroup.Pilot (LA missions sometimes use this note for who is speaking) and the color that the message will appear as.
You have four triggers at your disposal, and although the copy and paste buttons aren't there, you can still use the buttons on the toolbar or the mouse. The Delay works as expected and is the number of seconds after the trigger is fired that the message is sent.
Because XvT can be multiplayer, you can also define which teams will see the message. Just use Team 1 for normal missions.