I use an outsourced Exchange provider (mailstreet) and for a small monthly fee they add their spam defense software which eliminates nearly all of my spam.
Prior to that when I was using a regular POP email, I would use SpamCop.net - Beware of cheap imitations
which let me forward all my email into a special spamcop address, and out the other side I would in turn forward the cleaned email to my Blackberry. This solution worked nearly as well as the spam defense that Mailstreet offers.
Never give out the basic email address assigned to your Blackberry. So far as I know, in that situation there is no practical solution for removing the spam.