As far as data, The iphone uses A-gps, which is a combination between true gps and estimating your location based on cell towers. Thats why the iphone gps is an approximation of 100 feet. When it uses the cell towers for location it will use a little data, but I would bet it's a very tiny amount. The most data intensive part would be the mapping portion, and email/facebook/twitter updates, but with all this I can't imagine it being too much data for a 200mb plan a month