Trying To Prove My Parents Wrong. Help Me Out In Proving My Point?

You do seem very mature for a 13 year old. Creating a budget before spending your money is always a good idea. However, I would also caution you to listen to your parents as they can probably help guide you better. I would recommend going with them to the AT&T store and discussing the costs with an actual representative. I've added a link, though, to the basic costs.. It's about $50 per month for data and unlimited text plus the cost of the rate plan. I don't personally have an iPhone, so someone else can possibly give you more exact info.