I've been using this for Geocaching for about 8 months now. In the early days I struggled with it until I found the rght software to use and was thinking of spending mega bucks on a 'proper' GPS - but then I discovered Trekbuddy software and Mobile Atlas Creator, both free to download.
With premium membership I get updates of new caches and download pocket queries as gpx files. I use Mobile Atlas Creator to create map books in which ever format and scale I require and for which ever area I am caching in - it's so unbelievably easy to use! I load these into my Trekbuddy software and away we go, with map or compass view.
I have the standard 8GB card that came with the phone and I get really fast tracking and map views.
I get incredibly good gps, spot on or within a couple of metres every time except in really dense tree cover. Battery lasts around 5 hours on a trail.
I pay £18 a month to Virgin, incl unlimited internet.
237 caches later and I can't see any need for a Garmin now!