This is an Arma 3 Eden editor tutorial on how to create custom side chat and sound clips.
Copy & paste the following into the triggers on act...
s1 say3D ["hometime", 1000, 1]; showChat True; s1chat sideChat "Is it home time yet?";
s1 = unit name who is speaking.
"hometime" = what ever you have called the sound clip in you mission folder/sounds .
s1chat = what you have called the headquarters module that refers to either a unit or a fictional HQ/person(s).
"Is it home time yet?" = what you want displayed in sidechat at the same time as sound clip.
Link to the description.ext file in my dropbox (copy this into your mission folder):
https://www.dropbox.com/s/j0w6x0m1ml2...