Yeah, I was going to chime in and say that the people saying their cell phones made noise on "speakers" were using the wrong word. It's actually the phone interacting with a poorly-shielded amplifier that makes the dit-dit-dit noises. Example: If I put a cell phone in the trunk of my car near the amps, I get the dit-dit-dit noises, but not if the cell phone is in the vehicle cabin.

I also wanted to say how utterly hilarious it is that they put that little dit-dit-dit noise into Grand Theft Auto IV.