Getting rid of Spam: Any ideas besides switching to Gmail?

It seems that everyone's answer to dealing with Spam on their Berry is to open a Gmail account and either filter everything through the account (keeping the other account as your primary) or just give up and switch entirely to Gmail.

I have an email account with MSN (note: I'm NOT talking about Hotmail) through my ISP. I've had this account for several years now, and I would really rather not switch everything over if I can avoid it. At the same time, good old Microsoft won't let me forward my mail from my MSN account to Gmail, so that method isn't an answer, either.

I've found an on-device software app that will, supposedly, do the job. But after my IM+ mistake (JiveTalk works soooo much better lol), I'd rather get some other opinions and suggestions from the Crackheads out there.