I've had a look at a few of the 4WD GPS related iphone/ipad apps over the past couple of weeks and think that the app called Bit Map is well worth a look. There is another app called GPS MotionX which seems quite popular, but I haven't looked into that one yet and not sure what the quality/cost of maps are.
The good thing about Bit Map is if you already have any digital maps like Hema, Geoscience etc... that have the oziexplorer ozfx2 and ozfx3 map images with associated .map files, then you can quite easily use these with Bit Map. So no need to purchase additonal maps - Bonus!!
You can use other map images with Bit map but it is a little more involved with getting them into Bit Map. There is documentation on how to do this though on their website.
This app is very similar to OziExplorer but no where near as feature rich. If all you want to do is show your location on a map, log where you've been and enter waypoints to use at a later date (eg. following a previously recorded route and/or waypoints) then Bit Map does just that. You can view your recorded routes and waypoints within bitmap or view them on a PC using Google Earth. The routes/waypoints are stored as KML files as used by Google Earth and can be sent from your iPhone to an email address and then saved to your PC for viewing. I'm pretty sure you can do this through iTunes using the file sharing option too. You can also import KML file from Google Earth into Bit Map.
I normally just use OziExplorer when out 4x4ing on my HN5, but wanted something cheap and simple on the iphone for any impromptu offroading that may occur when I don't have the HN5 with me and then be able to record where I've been etc and then use this recorded information importing the KML into OziExplorer when back home. This seems to suit my needs just fine.
Have a look and see what you think.
Bit Map costs $4.99 which is quite cheap really if you already have maps to use.
Here is the website for more info.
http://nixanz.com/ios/bitmap/
Cheers,
Darren