You need to have the BlackBerry data plan on your account. Regular mobile data will not provide BlackBerry data services.
If you don't have BlackBerry data plan, add it to your account. If you do have it, do the following:
Try a hard reset. That is a battery pull with the power on, for at least 30 seconds.
If the hard reset doesn't fix it, call customer service and have them check you account and then resend sevice books to the handset.