[GPSNavX]

I would assume MyFi triangulates between cell towers. As such the accuracy would vary wildly and certainly be virtually useless away from land. iPhone 3G and iPad 3G have a GPS receiver so it is not dependent on cell tower triangulation. One does not need to have cell service (i.e connection or contract) to use iPhone 3G or iPad 3G GPS functionality. As such for iNavX use we recommend the 3G devices. The other option is to use MacENC or GPSGate on a Mac or PC to broadcast an interfaced GPS data to iNavX over WiFi.