If you have the OEM SAT radio option (prewired or actually installed) you have three wires in the connector which usually holds the wires for the CD changer. Without SAT radio installed or prewired, you don't have these wires and likely not even the connector (as in your car). The SAT radio is not conly connected to the head unit (the three wires I was just talking about) but also to the CAN-BUS and power (in the back of the trunk where it is installed).
I would still get the adapter with support for a CD changer and phone. This way you have all the wires you need eventually.
I would still get the adapter with support for a CD changer and phone. This way you have all the wires you need eventually.