Try a hard reset first (that is, remove the battery for about 30 seconds). If that doesn't fix it, navigate to Host Routing table in advanced options, select menu, and "register now.". If that doesn't work, go to your service providers BIS portal on a computer and resend service books. You should get a confirmation. If you don't, call customer service.
By the way, sometimes it takes a little while if you just had the blackberry data plan activated.