For prepaid sim cards you either have to get the 9.99 unlimted data or 24.99 unlimited data for smartphones. Many phones are detected presumably by imei lookup as smartphones but some like my e71 I can still use the 9.99 plan on. iphones and blackberrys are definitely blocked on the 9.99 though in my personal experience. I have an iphone 3g and BB 8320 that I also use for dev and testing on t-mobile prepaid SIM, and they are both blocked for internet(I just use wifi on those now for testing)