Ok so my first month I went over my 200 mb data plan!!! I was "new iphone 4 happy" and went over and was promptlt charged by AT&T. So now I am better but don't think I have the hang of it. Now I have a strict 200mb, so from what I understand, if I am home using Wi-fi with 3G disabled I wont use data from my 200 mb pool? I usually leave 3G off always even when checking my email and browsing the net from my car. I do believe that it still uses my 200 mb if data when I am mobile (with 3G still disabled) and not in wifi range right? I am not sure exactly what disabling the cellular data on and off does? I tried to disable it once, but then it keep giving me popups that it needed to be on to do anything! So thats it I leave my 3G off and wherever I go I try to connect to the wifi with the cellular data on. I have limited my MMS texting with attachments and youtubing and this seems to be a good reduction in data usage. Although I am good to do that stuff on wifi without using data right? thanks for your suggestions.