What address is being spammed?
If the blackberry.net address, you can only add filters to the BIS site, no real spam protection other than that.
If POP3 addresses, etc.., filter the spam at the email server end.
My advice, don't use the blackberry.net address ANYWHERE.
Oh yea, and the spam filter application by ANTAIR for BlackBerry Spam, find them here: http://www.blackberryforums.com/www.antair.com