Check out Peoples IDD & Roaming SIM, HK based but of course works in greater China: http://www.peoples.com.hk/p_prepaid_sim_iso.jsp
I know they do mobile data service as a value add (check the 'Charges' page for the detailed info), and they were the cheapest provider I could find when I visited last year. A single $76 HKD card lasted me for two weeks using voice calls *and* internet, and I came home with some left on it.
Whether they do BlackBerry data, though, I don't know - sorry. :(