[QUOTE=M.Mars]The problem is that iPhone doesn't have downloadable maps, so that when you find yourself outside of 3G coverage on at&t ( which is fairly often i know) you are out of luck./QUOTE]
This is not exactly accurate. There are several GPS programs such as Tom Tom and Navigon that have the map tiles loaded onto the iPhone so therefore cell reception is not necessary. I have used my iPhone 4 in the car for hours while playing music or streaming Pandora without any problem. However, they will overhead stuck inside the map pocket of a tankbag on a warm day.
Long story short they do work however are not best suited for moto use (however you can get by.)