Don’t starting putting money away just yet, but Engadget is reporting a Dutch rumor that TomTom is working on a GPS module for the iPhone. No further details are available at this time, but from the picture it seems as though it would be an add-on device that plugs into the docking port on the bottom of the iPhone — the same place you plug in the charger.

Although there’s no hard evidence, Engadget does point out that the highway depicted on the photo is a favorite for internal TomTom test studies. Also, we know that Apple is opening up the iPhone to third party development in February, and we know that some companies have received an early copy of the SDK in order to get a jump start on development. Certainly TomTom, as one of the leading GPS companies, would have received a copy. So although there isn’t any indisputable evidence, this one is certainly a possibility.