I found this and it worked for me. It wont 'push' the email like gmail, but I have it set to pull every 10 minutes.
Go to manual setup > IMAP account and change to these settings....
Imap server - imap.mail.yahoo.com
SMTP Server- smtp.mobile.mail.yahoo.com
My yahoo mail was working fine then it just stopped working about a month after I got my phone. I just tried this and it working great! Thanks:biggrin: