Non yahoo plus must be set up manually as an imap.
Start by entering your address and password as usual, you will get an error prompt, choose manual setup, choose imap...
In the top box for the incoming server info make sure in the first box the id is the full address including @yahoo.com
In the incoming server box enter: imap.mail.yahoo.com
Scroll down and hit Enter, the program should process the shift to the outgoing info screen
In the top box enter: smtp.mobile.mail.yahoo.com, scroll down and hit Next....that should do the trick for ya...TBV