so just after reading about half of thread with the iphone and geocaching etc ... what i will say about the phone (as i have been using it before the release of the iPhone 3G) is that its great to punch in the coordinates to google maps to see roughly where you need to be and what the area looks like via sattelite etc
after that VHover10 and myself use our Garmin GPS device to find the cache ... when we cache without the phone we find it much more difficult because we only cache paperless style
so we use my phone to look up the cache in google maps and then in the web browser to see roughly the area that we are heading too... and then we use the OTHER GPS device to find the actual cache.. we find this the best way that we cache and find stuff
cheers
