You can use the wifi only iPad for moving map but you will need to by the Bluetooth GPS to go with it.
This is not a bad option even for people with the 3G version as you can leave the antenna where it can get a good signal for example outside the cabin on a boat and still use the iPad inside.
I have been looking for an app that turns the iPhone into a Bluetooth gps antenna and there doesn't really seem to be one. Hopefully it's only a matter of time but it might be a limitation of the Bluetooth/iPhone.
Mady