I just learned today that there is no way of automatically configuring the Blackberry through a policy to allow the call display to work while locked. You can force the policy so that a user can NOT enable the display of the contacts while locked, you can’t do the opposite. As you can see from the screen shot below I’ve highlighted the *NOTE* in question.
*BOTH the admin AND the user MUST allow the address book to be excluded from content protection. Otherwise the address book contents ARE CONTENT PROTECTED.
To allow the contacts to be excluded you must either have “False” selected.
Next on the Blackberry hand held you must follow these steps:
Options -> Security -> General Settings -> Include Address Book –> set to "No"
For the Full write up on the policy: