How to persuade your mom to get you a blackberry?

It is for my graduation. Originally, she was going to get me a $130 wallet, but now I realized I don't really need it. At the moment, I have a really crappy phone. Like, scratched, dirty, paint on it, etc. Some of the buttons don't work. So, I want to ask for a blackberry. I found a nice one for $165. My mom is all like "You don't need a new phone", "How will I know you won't wreck or lose this phone?" etc. I'm really bad at persuading, and arguing, so what do I say? How do I persuade her?