okay so I went to get the iPhone 5 last week from a t mobile shop in Florida and the down payment said $150 if you have "perfect credit" and im only 16 so my grandma has to sign the "no-contract" papers and well she had "good credit" so the down payment is now $300 and something plus other charges came out to be $412 up front and I didn't have enough money for the Down payment untill now keep in mind my dad is paying for my $70 a month unlimited talk, text, and Web, so they said that my dad will continue paying that but my grandma is obligated to pay the phone off.. now the guy said since im paying a higher down payment of $300 that I only have to pay $12 a month in stead of $20 a month for 24 months, now I plan to pay it off in full by next week, a total of $650 now my question is since im paying $412 up front. will I owe $238 or will it be more since it was (other charges) that increased the price so much ?