Phone module:
- Under the driver’s or passenger's seat under the carpet.
- In other cases it is in the trunk, but can be also behind the front seats (cabriolet or sport version cars).
CD changer:
- It is mostly in the trunk, sometimes in the glove box, in rare cases in the center console.
- BMW: If the CD changer connection is too far in the car (in the trunk), then you can use the extension kit (EXT1GW2) for the installation, which makes it possible to place the hardware of the Gateway to the front part of the car, into the glove box for example.
As an example here is an old Audi 6CD changer and a Porsche phone module.