These devices that are installed into your automobile allow drivers to make and receive calls from their in-car Bluetooth system. They either come factory-installed or anyone can buy an aftermarket product. It is no like OnStar, OnStar forwards drivers calls to a car in side the car, not the cell phone. Bluetooth is operated either by the car controls or by their hands-free voice activation. This is very handy. It even mutes your radio when a call is answered. Over thirty automotive companies are offering Bluetooth compatible vehicles.