I did this because I sold my iPhone a while ago. I kept using the dumb phone until I heard about the new AT&T plans. (Which suck btw) Today I stuck the SIM card into my mom's iPhone and it worked without me plugging it into iTunes, so I assume I'm still on the iPhone unlimited data plan? I kept the SIM out and I think it will stay out because I don't want them to take off my data plan because I'm using a "dumphone." Does this sound right?