It's been a while since I've watched this movie (TBH didn't even watch it all, I can only take so much of Demi Moore before I have to change the channel) but IIRC the comm devices they used were these patch like things stuck to their throats that they just pressed against while speaking. If I am remembering that right, that would never work - you'd only end up sounding like Charlie Brown's teacher. "Wah wah waaaah waaah wah wah waaaah." Speech is shaped in the mouth, having the device on the throat would only give you the sound of the vocal chords vibrating.