You have to have cell phone service for the GPS to work on most phones. I have a Motorola Droid - the google earth on it is really nice, but as soon as the phone service is gone, so is the GPS service. So, it doesn't work real well in remote areas and certainly won't be replacing my Garmin for hiking.
you don't need it for the Nokias, which is the big difference to the Android. I won't get one, because in general I think phones should be used as phones and nothing else, but I can see this becoming a standard feature you won't be able to not have on your phone in the near future.
