Make sure that you are subscribed to a BlackBerry data, if not please see this link, your network name on top left of your home screen should be in capital letters like 3G, GPRS, EDGE etc. Not lowercase (3g, gprs, edge)
If you’re subscribed already and can’t connect or use any application, please do this
Options > Device > Advanced Settings > Service Books > Delete everything
Some can’t be deleted, just leave them alone.
After deleting everything on Service Books, remove the battery and put it back again.
Now try using your applications.