Quote from Fiat's press release that I mentioned...
The system automatically lowers the volume of the radio, and allows occupants to hear the caller through the stereo loudspeakers. An integral, echo-cancellation device maintains sound quality without any deterioration in timbre, thus preventing unpleasant, metallic tones. Moreover, the Bluetooth system is operable not only in the presence of a radio, but also when only the wiring is installed, hence retaining radio unit choice for the customer.