[PoorMansCamaro]

http://www.onstar.com/web/portal/systemdetails#onstar

OnStar System
This system is responsible for the operation of your OnStar system.
[+] Wireless Communication System
[—] Close Wireless Communication System
The communication portion of the OnStar system uses a cellular device and cellular networks to transmit voice and data from your vehicle to the OnStar Call Centers. OnStar is different than an average cell phone. In outlying analog cellular networks, OnStar can use a much stronger signal to make a cellular connection. Your OnStar system also has the capability to use several different cellular networks to make a connection to OnStar. If a problem is detected, the red light next to the OnStar buttons will turn on. That information can also be sent to your OnStar Vehicle Diagnostics check to alert you that service is needed.


[+] Global Positioning System (GPS)
[—] Close Global Positioning System (GPS)
Your OnStar system uses a GPS receiver and is continually calculating your GPS position as you drive. When you push your OnStar or Emergency button, or if your air bags deploy, your vehicle is designed to send your GPS position to OnStar. By sending your location, OnStar Advisors can request that emergency service providers respond to your location. If you have the Directions & Connections service plan, Advisors can find businesses near your current location and can provide you with driving directions to just about anywhere you want to go. If a problem is detected, the red light next to the buttons will turn on to indicate a malfunction. That information can also be sent to your OnStar Vehicle Diagnostics check to alert you that service is needed.


[+] Peripheral Systems
[—] Close Peripheral Systems
Other components in your OnStar system like the buttons, microphone, and antenna are continually monitored to ensure proper function. If a problem is detected, the red light next to the buttons will turn on to indicate a malfunction. That information can also be sent to your OnStar Vehicle Diagnostics check to alert you that service is needed.

so i guess it could be any of those...