On Star with aftermarket a/v devices

[rvs9]

I am having the Eclipse AVN 2454 installed with some other goodies. The installer told me that he would mount a small speaker for the On Star output under the dash as it would have to use the stock amp. I told him that I believed a device was out in the market that allowed On Star output to be routed through the driver's speaker and would mute the aftermarket audio when On Star was in use. I have spent the last hour searching here for the post where I thought that I had read about it, but no luck. Does anyone know the link to the post or the device. Thanks!