Two things to try.
First, on your BlackBerry, go to ( Settings/Tools -->
) Options --> Advanced Options --> Host Routing Table
. Click the Menu
button and select Register Now. You'll get a message that the request was sent, and then receive an email with the subject Registration. Now try it.
If that doesn't fix it, go to the Sprint BIS site
, (create an account if you haven't already), then click Service Books
on the left, then click the Send Service Books
button. You should get the necessary service book at that point.
If you don't, you'll have to contact Sprint customer support!