How to get my stepdad to buy me an iPhone?

I know this sounds pretty stupid but how can I get my stepdad to buy me an iphone? He bought his daughter a gold 5S yesterday and I'm pretty jealous because I would at least like something similar. I don't have much and my mom doesn't wanna spend $600 for a phone. I receive good grades and she does "ok" in her classes. How can I convince him to buy me one without asking and sounding stupid?

You can't

Christmas or birthday is most resonable, sit them both down and talk about it. They would understand if it would be of the two.