I used to have a working iphone 2G with AT&T data plan. After I downgraded it to a Nokia regular phone, I jailbroken my iphone 2G. I can use it without SIM card. Now when I try to insert an AT&T sim card (the one which works fine in my Nokia regular phone. without any data plan), it reads "Different SIM detected, please connect to iTunes". So what should I do to continue to use it in AT&T network without a data plan?