I have a iphone 4 I just purchased and I have a question about the data I use......How do you know if you are using wifi or not.......My phone has my wifi listed so if I'm home I am not being charged for the data I use, is this correct??? Also if I don't sign out of aol and facebook but is not using it, I am not charged for the data use.........Hope I have made my questions clear, I am new!!!!