She is on a really old Cingular plan. only pays like $35 a month. I want her to use my old iphone 3gs as she has a super old flip phone with only 450 min and 5000 n&w min. I tried her old sim and it still works on the iphone (making calls) Would AT&T charge her the data feature and change her plan or can she just use it as a phone and have wifi for her "data" . She never goes out and about so she will never use the data plan anyways. Thanks!