Hi guys,
Let me preface this by saying I use TomTom and have not tried Navigon. I chose TomTom based on the lack of accuracy of the built in GPS of the iPhone and that they had a car mount that boosted the GPS.
I had thought Navigon didn't have access to the car mount GPS boosters. If that's the case doesn't your phone get confused sometimes especially in cities or sometimes put you on access roads on highways? If I don't use the booster it does that consistently since it's not that accurate.
That is very interesting, I thought iPhone had built in GPS chip to work as a navigation device.