In case anyone out there is interested in iPhone nav apps, I'll tell you about a few I've been using. Please don't let this thread degrade into a 'you shouldn't be using mobile phones for nav' and 'you should be able to read a map', etc. I can read a map and use a compass, thank you very much, and I always have both when I'm out in the hills. In fact, I'm pretty damn good at micro nav and have plenty of experience in whiteouts and low cloud in the Scottish mountains and the Alps, so lets put that one to bed now.
However, sometimes I like to play with other nav gadgets like my Garmin Vista HCx and my iPhone 3G. All of the following iPhone apps are available through the iTunes store.
The first app is 'NavFree', a satnav app for UK and ROI. It's free and it's based on Open Source Mapping (OSM). This means it isn't quite as reliable as, say, OS mapping, but it's getting much better and I have had few problems with it. For free, it's brilliant! Be aware that it is nearly 500mbyte in size so make sure you have a wireless connection to your phone when downloading, or download to your computer first and then transfer it to the iPhone. I got a car charger and phone cradle on eBay for £5 and now use this whenever I need satnav. Excellent.
The second app is 'Outside Maps'. It's free and allows you to download OS map tiles so you can use them later offline, without being connected to a wireless WIFI or 3G system. Download the tiles you want and then delete them afterwards to maintain memory on the phone. The app also allows some rudimentary navigation.
Finally, 'Maps 3D' allows you to load offline mapping, based on OSM, and - I love this bit - shows it in 3D too so you can see what the terrain actually looks like on the ground. Love it! It's geared towards biking but is use as applicable to hiking/walking. There is a free 'Lite' version or you can pay a measly couple of quid for the full version.
Looks like Apple are also going to release some 3D mapping software soon too so look forward to that!
Hope this helps anyone looking for cheap/free mapping apps for iPhone. There are lots out there but most are garbage and these three do genuine work and have worked well for me.