One of 2 things can sometimes fix that.
Switch off all connections then restore, or a battery pull.
You might also find that the handset has not been registered on the network yet. Have you had the welcome text?
Failing that, do a search on here on resending service books.
You can register the device by going to Options>Advanced Options>Host Routing Table>Menu key>Register now.
Could be worth resending service books, you can either do this from your carrier's BIS site or from the email set up icon on your device ( envelope with a cog on it ). Either way enter your username and password, the "send service books" option is under the Help heading.
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