If your carrier's network is up and running and you have BIS service with them, you should then resend your service books. They're basically an instruction manual for your phone to know how to access the network and use your phone's features.
This article will tell you how to resend them.
http://www.blackberry.com/btsc/KB15402
Let us know if that helps you. 
It's never a bad idea when switching to a new carrier, due to travel, to resend your service books. Your phone is supposed to do it automatically when it detects that you're roaming, but not even BlackBerry phones are perfect. Close to it, but not quite perfect yet.
Those service books tell your phone how to do its job. The chances that this will correct your problem might be slim but we've got to start somewhere.
Get back to us with your results.
Let's test your network connectivity.
From your homescreen, go to Options>Device>Device and Status Information. When on that screen, type in "test" (without quotes). There will be no field in which to enter it and nothing will appear while you type. Just type it in. Click OK to start testing, then press the menu key and select Start. You don't need to be guided through the test, so click No there. Scroll down to Network Connectivity, check the box beside it and click Run at the bottom of the screen.
Get back to us with your results.
