[GPSNavX]

Found this and have not tried, but it appears you can setup your iPhone (w/ iOS 4.3 or later) as a Hotspot. Once that is done and iPad or other iDevice tethered to the Hotspot will also get the GPS information. So an example would be iNavX running on an iPad WiFi model, with the iPad WiFi tethered to the iPhone 4 Hotspot. More info ..

http://www.cultofmac.com/wifi-only-ipad-...hone/86642

Still I would recommend getting an iPad 3G which includes a stand-alone GPS receiver as opposed to the WiFi only model which does not include a GPS receiver.