A TUAW reader posts the following video stating that a new interface found in iPhone OS 4 allows for navigation that would be optimized for automobile use.
Our source says that information bundled into the application shows that Apple intends this new “iPod out” functionality to be used in automobiles using the iPod Accessory Protocol (IAP). Hints as to this use are found in strings within the application itself. These strings include IAPSimpleRemoteCarButtonNotification and IAPSimpleRemoteCarButtonTypeKey.
Also found were frameworks (kCTCallStatusChangeNotification) which would handle call routing. From the interface.
This might also be freaking awesome for the iPad as well.