ok,,i have to say something..
15$ dataplan for dumb phone or basic phone is the same data ur going to get with 200MB or 2GB...so why dont after downgrade to 15$ data for basic phone then just use that with ur iphone.....yes you will get text saying that you need to upgrade blah blah blah but just ignore it and once awhile just use ur sim with basic phone..if the rep called you..you can tell them that you are using the basic phone but sometime borrow iphone from a friend to test out..
Will att forces you to update the 200MB or 2GB data plan ?
Nope..but they will text you and call you.
I have done this. I went to Att store, first time ever to open an account, when i open i told them I will have the family plan, and i will use my old phones. and I will add 30$ data unlimited + text unlimited for family, They will ask you what kind of phone you have, I told them it is the phone i bought from china, just regular phone, so They added the package. Later on i went home i use the sime with my other Nokia SmartPhone, and you will get text and called from them but depend on your social skills, but what i mean is that you can use your 15$ data unlimited for basic phone on smart phone.. data will be just the same.
and for people use the method at 1st post didnt get the text , YOU SHOULD NOT PLUG THE SIM BACK TO IPHONE4, after you call to downgrade and change plan to 30$data unlimited + unlimited text, please use your sim with dumbphone untill you get the text , you will get in in 1 to 2 hours the most if the sim is in non smart phone.After you get the text which basically mean you data is activated then you can swith back to your iphone.