The Google Maps app is just that, an application, a piece of software that you download to your phone. When you open it up it sends and receives data, this is what ATT charges for, the actual data transmission. If you have a smart phone / 3G phone you are probably already paying for data. If your phone has a GPS in it will probably also work here and identify your location, assuming Google Maps supports that phone. If you buy the ATT nav software you are basically paying extra for what should really be a free service.