Hello and welcome
From the Help file:
Voice
Aces High II provides built-in voice communication software to allow players to talk over two different voice radios while online.
The first radio is the tunable radio where players may talk privately to squads or any tunable channel. The default transmit key for the tunable radio is key "T".
The second voice radio is the range radio and it is not tunable. The range radio allows transmission to those in icon range if you are in flight or players in the room with you if you are not in flight. The default transmit key is "F12".
All players on both radios are listed in the Voice roster list that appears whenever the radio bar is open or if the player's location is in the Tower. This roster list may be positioned anywhere on the screen.
I think a read over of the help file is a good thing to do for new players. You can find it here:
http://www.hitechcreations.com/frameset1.html?download.html