In reply to phja:
ViewRanger is good for the price, although the functionality didn't seem intuitive to me. I don't use it often - if at all - but it's good as a backup if my map and compass get lost, blown away or my skills go awry.
I paid £60 I think for 4x50k mapping sections to cover all of Scotland. When you switch it on it gives you a clear indication on the screen map where you are, that alone is good enough for me.
One to remember is outdoor GPS are designed for the outdoors and mobile phones aren't, the problems come with weather, battery usage and ability to withstand the knocks and bumps - get a case to keep the phone in.