The radio/chat messages does NOT work in the intro section. I cant tell you why but this is a fact.
For what you're trying to do (talk with the officer), radio chat is definitely not the best way to do it (you dont radio a guy that is right in front of you, dont you).
Use the titleText command (check the com. ref.) to write text in the middle or at the bottom of the screen.
If you want to use some sound files (ogg) you should check one of the many sound tutorials that are available on OFP editing sites.
Cheers