My family is thinking about going to AT&T and getting a family plan. My dad and I would both get iPhones (I would probably get the 16 GB 3G S and he would get the $99 3G) and my mom would get some basic free phone. Does this mean the total data plan would cost $60 per month ($30 x 2) or do you only have to pay one $30/month fee regardless of how many iPhones you have on a family plan?