Cell phone and GPS antenna are on the rear of the roof.
The splitter (actually a switch) is used for the backup teleaid antenna in the rear bumper.
If the car ends up on it's roof and can't connect to the teleaid response center, it will try switching to the backup antenna.
The GPS antenna being upside-down will make no difference as the teleaid control unit sends in the last known coordinates of the vehicle along with the last known vehicle speed and direction when the call was activated (activated either automatically via the SRS system, or by the owner activating one of the 3 teleaid switches) so it doesn't really "need" to use the GPS antenna to give the teleaid response center some useable info.

Gilly