OnStar® Microphone
WARNING: This page is about a different car, the 2002 Buick Regal and 2002 Buick Century. However, it is still accessible from the selected car via links, so may be relevant.
The OnStar® microphone can be part of the rear view mirror assembly or, on some vehicle lines, can be a separate unit. The users voice is transmitted from the microphone to the VCIM over the cellular microphone signal circuit.