How to remove an IT policy from a Blackberry
1. Upgrade your Blackberry to OS 4.5 or higher
2. Backup your device using the Desktop Manager and then close Desktop Manager.
3. Go to Start->Run and type CMD
(you can also find the command prompt in Programs >Accessories.)
4. In the command window type the following including spaces:
cd c:program filescommon filesresearch in motionapploader
or if you are using 64-bit Windows 7, type
cd c:program files (x86)common filesresearch in motionapploader
5. Now type: loader.exe/resettofactory
6. After your device has finished restarting, you can use the desktop manager software to restore all or some of your data.
from : http://www.blackberryforums.com/rim-software/67224-remove-policy.html