I'm using the Apple Store app to practice buying my 6S for tonight at full price, keeping my exisiting plan with grandfathered unlimited data. I'm going through all the steps with a regular iPhone 6, and when I get to the page to select a data plan, and it isn't giving me the "Keep existing plan" choice. I can only choose to keep my base and messaging but the data plan part is asking me for one of their new data plans! Anyone have any idea what to do here?