Oh. That's annoying. I don't know if your ports will be different on a different phone (I have a Galaxy S)? I just left mine at the defaults (which are the values I wrote in above). It might be you need to try those IMAP/SMTP settings with the default ports for your phone (i.e. the ones it has in when you first come onto the set up screen).
Another possibility (and I hate to ask...

) - for username, you're just putting what comes
before the @yahoo, right?
(I know, I know, but I've made the error of including the whole thing before now...

)
Otherwise, I really don't know. I fiddled around with my settings for ages before I got these to work, and even now it won't work half the time if I have wi-fi switched on. So it's not as if I actually really know what I'm doing!