I am an existing ATT customer. My current contract is not up yet. If i get an iphone what do I have to pay for (besides the phone itself)? I saw that theres aplan for existing customers. Where you had on $20,30,or40. I am currently under a plan with my dad where his is 59.99 and has me as an additional line for 9.99. How would I got about doing all this? 