I used the Blackberry 8700c but found the technology for trading(device and broker software) a bit clunky for anything other than getting quotes.
I was hoping to have it as a backup to my desktop connection as well as a means to be able to trade when I couldn't be at my desk, but I think we're a few years away from that yet.
Quotrek works fine on it, but I sometimes had trouble connecting to the feed. Since the Blackberry data service plus Quotrek amounts to $65 a month, I didn't feel it was worth it.