Was it rude/wrong of me to have said this?

I was sitting in the class and using facebook(I was bored and professor wasn't in the class).So this random dude besides me says to me: "I guess you use your iPhone 5 just for facebook and calling, right? Why did you have to buy such an expensive phone if you only did that?"
Me: Excuse me? Why do you even care? Did you have to pay for it? Anyways, I didn't buy iPhone 5 but I got it as a gift from my parents for getting into this prestigious college.

You didn't do anything wrong, you were just standing up for yourself

I wouldn't say it's especially rude but the part where you said "for getting into this prestigious college" was certainly wrong because of who your audience was--namely people who were in the same college. For example, even though I'm not the guy you were speaking to, I now somewhat dislike you for what you said.

Well depends on the way you both said those responses.

No, I talk that way to people when they're being smart asses with me.

Yes. It was rude of you to answer the random dude in such a way, but then you already knew that or you wouldn't have been worrying about the whole thing. The dude was rude to start with, but maybe he was just trying to start up a conversation. Some people are a bit lacking in social skills, perhaps you might wish to work on yours…

Be careful, college time will pass bit Facebook will be waiting and available even after classes. You must not be on Facebook during class hours. You should mot worry about being rude to the dude, you should worry about what you choose to do in class. This will click when you fail exams.

You weren't rude at all. You were also not wrong for saying what you did. He was rude and wrong for making assumptions about you, offering his opinion in such an attacking way and not minding his own business.