Try doing the PRL (preferred roaming list) update. Following the steps below.
Dial *228then press SEND(the button used to initiate a call).
When prompted, press 1(one) to begin programming.
Wait for up to 2 minutes while the network links your service with your phone.
When programming is complete, you will hear a confirmation message and the call will end automatically.
Power-cycle your device to complete over-the-air activation.
In addtion to the recommendation for updating your PRL, try a battery pull. A simple battery pull to reboot your device can sometimes clear up many little problems with a Blackberry.
Use the Desktop manager and update the software, or if there is no update just reload the phone. Make sure to set desktop manager to back up your device, and to delete all apps and app information (just to clean out the possibly corrupt data).