Bob it does not use cell data on the phone.... It's quite similar to a wireless router for your computer. You are putting out a signal from the trunk or wherever you mount it. That signal is received by your phone or iPod wirelessly and whatever your doing on phone/iPod works trough speakers. Ex. I play a song on IPod and it plays through speakers hooked into amp. It also works if you get an incoming call! The siganl is localized to about 200 ft.