To better understand your question - are you planning on getting rid of your BB phone? If so, then Options> Security settings > General Setting >{Menu Button}> Wipe handheld
Which will clean EVERYTHING on the phone and the easiest.
Now if you keeping the phone than move your contacts on your outlook (or what have you) to another folder like a pst, and then synch it... all your contacts will disapper.
This information was found on the Internet. Good Luck
You should be able to clear them out using DM. If you go to advanced backup and restore, you should be able to clear individual areas of the phone there.