Rooting the phone will not give you free data. It will let you do things like tethering and blocking ads and removing unwanted programs, but your data usage is controlled by AT&T at the server side of things. If an exploit was found that would let AT&T phones use free data they would lock it down lickity split the Cell carrier can't control your phone so what they do is control your access to their network through use of the IMEI & SIM card Numbers. It checks a database to see if your phone has access to a certain service. If it doesn't you don't get that service unless you activate it with them at which time you can expect a bill. You can however use WiFi for free till your eyes bleed on the phone without rooting it.