There are two Memory Map apps for the iPhone. The MM Free app works well, as you don't have to worry about old licenses, you just get the app, which gives you large scale base maps of 1:250k and 1:1million, plus 400sq km free. Then you set up an account and you buy 700sq km for £12, for any area you want, in 1:50k or 1:25k. There's also another app, I think called GB map, which is £4.99, which gets you the base map, plus free downloads of the OS 1:10k maps now released, for as much as you can fit on your phone. Viewranger are now on Android, and you can install the entire GB OS maps from the DVD if you have a copy, or, I believe, buy the app and download the maps from Viewranger. Sadly MM don't appear to have an Android presence, tho' I could be wrong, and they have this restrictive license issue. I've got Viewranger from my old N95, and I'll be putting the whole lot on my new iPhone in a few weeks time. (My 3G's totally full up).