What is the difference in battery life between urban areas with easy 4 bar cell reception and wilderness where you may have no reception? We went thru this exercise for another thread and determined that my iPhone 4S is not a good substitute for a real GPS. I'm using a Verizon iPhone 4S so it doesn't have a sim card to remove (referencing the link above). I'll stay with one of my Garmin dedicated GPS receivers and save the cell phone for communication.