Just for an idea (something that I have thought about doing myself) is just getting the new pioneer head-unit installed in my car. After having this installed, plug your iPhone in and run the app called MotionX GPS. The technology in the head unit is great (supposedly) and you can view the GPS of your iPhone on the head unit. One difference you are talking about is that you want a GPS... what I am talking about would have to be installed in your car. Thats all I got.
I have the older model of
this in my truck, and I would probably purchase this unit but any of
these models should have the "App Mode."
This is what the pioneer website says about the technology..."With App Mode you can enjoy listening and viewing the content on select compatible apps directly on the receiver's display from a connected iPhone or iPod Touch. Limited controls such as track forward or reverse may be executed from the receiver."
Hope I could help!
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