I'm not exactly sure what your issue is.
Evolution and Firefox's email client works much like outlook as far as connection purposes are. And you can always go into mail.yahoo.com. If your having trouble with these please be more detailed so we can understand better whats going on.
Yahoo messenger does have a Linux version but it is rather striped down. You can connect to yahoo messenger via third party clients like Pidgin, kopate(spelling) or many others. Pidgin is able to connect to yahoo chat, and there are others that can too. You also can get basic messenger functions off a site messenger like www.meebo.com
Now if you want voice, I have heard some linux yahoo clients allow it but its difficult I believe. There is other options for internet voice such as teamspeak, but they have nothing to do with yahoo.