I my husband and I have been using unlocked iphones with an att sim card for several years now with no problem. One was a 2g and one was a 3g. A couple months ago my husband was given a 3g phone. He unlocked it and used it with the same att sim card with no problem. Today att sent him a text saying they had added a data plan to his acount since he is using an iphone. When I called them about it, they said that every time a phone call is made the serial number is transmitted to att and if it is an iphone the data plan will automatically be added. They said they will remove the data plan, but if another phone call is made from that phone another data plan will automatically be added. At this point att has not said anything about my use of an iphone. Has anyone else had this problem? Does anyone know of a way around it?