There's a ton of talk on this site about viruses, do some searches to see what others have said.
However, I'll answer you question directly. NO, final answer. At this time, there are NO KNOWN viruses for blackberry OS. The closest thing in existence would be what's called "flashing" and people don't do anymore cause it's not worth the hassle.
The only BB virus I've ever heard of was basically a Windows virus that would get uploaded to a corporate network VIA a BB connected to BES. That was more of a demonstration virus though, just to prove it's possible.
This is a hard one. I want to say no, but anything is possible these days. Most likely I think you would get it through an email or maybe im attachment.
