Did you have it setup in BIS, it was working, and now it has stopped? Or have you been unable to set it up period?
If the former, do a hard reset (with power on, remove the battery for at least 30 seconds). If that doesn't fix it, resend service books. How do I resend my service books? - BlackBerryFAQ
If the latter, then do you have a BlackBerry data plan? If so, then describe what you are doing, what you see, and any error messages.