Voice Feedback
WARNING: This page is about a different car, the 2002 Oldsmobile Bravada, 2002 GMC Envoy XL, 2002 GMC Envoy, and 2002 Chevrolet TrailBlazer. However, it is still accessible from the selected car via links, so may be relevant.
The OPC system has the capability of responding to the user with either an automated voice response or with a tone or "beep". These two types of responses can be switched back and forth by pressing the answer/end call button, waiting for the system to respond "Ready" and speaking the phrase "voice feedback". The system will then respond, "voice feedback is now on/off".