I can't be your kid ... just sayin'.
Kiddo, what I said was not negative. Your post reads like an update to your facebook page or blog. It had absolutely no question in there so perhaps in your attempt to defend your post you could have tried a little harder to post the very question you just asked. Let me help ... "I'm 19 with no credit and found out from a friend that I may have to pay a security deposit to get an iPhone. Has anyone else run into this problem?"
But like you, I like that no matter how obvious it is people will post threads that read like blogs, lack questions or basis for discussion, and then whine when they don't get the response they want. Example above ^^^^.
My answer, btw, would have been a link to other threads where people asked that very question. I would have then said that you may want to call or go to AT&T because your friend may be wrong. And then I would have made the comment about your parents.
Now, if you take that as negative then you're hypersensitive and no one will win with you. Unless of course I posted "OMG WTF BBQ that is HOOORRIDD! No wayz man! That suckz!" In that case we'd probably get along better.
Good luck finding out from AT&T but you'll likely need to pay a deposit for the very reasons you stated above.