It's fascinating that blackberry has moved from the phone of business, to the phone of the poor and youth.
Why do you think Jay-Z raps about/endorses it? If the answer is as simple as, "He's paid to," then surely he'd be rapping about other brands beyond the traditional Escalade/Cristal/etc. The real answer is that Blackberry is an inexpensive smart phone option that is not the "white and corporate" option. You've got an unrealistic idea of what poor and urban looks like and acts like.
A Blackberry IS an accessory, but only because it's considered a symbol of being part of a particular group, not because rappers endorse it.
"Real money buys Patek Phillippe." Give me a break.
Jay-Z is a businessman first and foremost. Kids don't care about Exchange integration or whatever. He namechecks the brands he likes (as far as I know, he has no official relationship with the brand) and his fans buy them. Same with Rolex, I don't think they have marketing arrangement with any rappers but they get namechecked all the time.
FWIW I have a BB myself, I am certainly not disparaging anyone else who has one...