See also:

Deactivating HDC
Press the button again and the LED goes out. HDC is automatically deactivated above approx. 37 mph/60 km/h. ...

Removing the mobile phone
  Press the button and remove the mobile phone. ...

HD Radio™ reception
Many stations broadcast both analog and digital signals. If a digital radio network is available, these stations can be received digitally and thus with better sound quality. License conditions ...