Only perform at the advice of a support agent. If the proper settings are not in place in the system, your phone will not know how to connect back to the provisioning server.
On the Home screen (back out a a missed call or new voicemail screen) hold down the center "OK" button for appropriately 10 seconds.
You will be prompted "Reset to factory setting?" Hit "OK" and the phone will reboot.
Do not reboot the phone in the middle of this process.
Contact support if you have issues with the phone coming back with the appropriate settings.