In the second dance battle scene in the club, Ice-T can clearly be seen rapping/talking into the microphone in the background yet we do not hear him at all. All that can be heard is music and the main characters dialog.
Towards the end of the movie when Kelly and Ozone are arguing at Venice Beach, the last shot of that scene as they are walking away; Ozone says, "I want to show you what real dancing is about." You can see that Ozone's lips don't move, but you can still hear him say something.
When Turbo and Ozone go to sit down after practicing their dance moves towards the beginning of the movie, Ozone is pulling out a cigarette of his pocket in the next shot as hes sitting with Turbo it instantly appears in his mouth.