iPhone, GPS , Maps

I've looked and looked for iphone apps that can use raster maps but the only things I found were US-based and downloaded maps directly from a server (google TopopointUSA and Fugawi). I haven't been able to find ones that you can supply your own maps to. It should be possible, but hasn't been done as far as I know.
There are many gps apps for the iphone though - so if you don't need raster maps (eg. hema 4wd maps) then maybe there's something else which does what you need with some sort of topo maps. (I've looked for these too, but not very hard as I want to use my hema maps).

Does the GPS component require the phone to be in range?
If not then it would be ideal for bush walking??

What I was looking at was to reduce the number of gadgets. Currently I have a Magellan explorist 600 and a tomtom 720
The tomtom works great, and woiuld be costly to use the iPhoine.

I was looking at storing maps on the iPhone (8gb storage), and then use the GPS component to track the vehcile when 4wding or bushwalking. If it does that then I can remove the Magellan.

Think the GPS comonent has been trahsed, yes it does work outside of range, just need to workout how to store maps on the iPhone