The app works on 3GS phones only and is OK for a rough idea of where the sats should be. There is a work around for the App. where there is no cell service. you have to go into the maps on the phone and wait till it locks onto your location (it wont show a map but will blue dot on the grid) then in 2-3 seconds switch to the app and it should work. i have had it work but it does take a few min for the map to load your location.