Another possibility is someone guessed your blackberry email address. Delete it, create new one that is hard to guess, like
![[email address]](http://www.blackberryforums.com/?emailimage=361594542cca5315a0abf41611c30e41)
and edit your forwarding rules to send to new email address.
That would definitely stop direct spam sent to blackberry, and only leave the one possiblity, which was suggested by rcbjr.