I am an existing customer with AT&T and I was looking at the rates for the iPhone at this site for the existing rates http://www.apple.com/iphone/easysetup/rateplans.html. I am wondering do I have to get the unlimited data and text messaging? I know its good to have cause the of the visual voice mail but do I have to get it? Or can I just buy it and continue with my current contract that I have with them?