Here ia an application that runs on your Q:
http://mobile.yahoo.com/go
This is ok, but not great.
I personally would suggest a service called mobipush
http://www.mobipush.com
It forces your pop/imap accounts directly to your phones pocket oulook via active sync.
That would require your yahoo account to have pop access. Which if you are just using a free yahoo account, then yahoo Go is the ONLY way that you can access your yahoo email other than just going to mail.yahoo.com from IE.