I found a post on another forum that helped me set up my yahoo mail on my Moment without having to upgrade my yahoo account. Here is how I get my yahoo email
Enter your yahoo email:
USERNAME@yaho..com
Enter Password
Then press Manual setup
Next Select IMAP account
enter user name: USERNAME
Password - should already be filled out
IMAP server should read
imap.mail.yahoo.com
port
143 (mine is 143...but it can be different, so leave it alone at first)
Press Next.
For smtp server:
smtp.mail.yahoo.com
port:
25
Hope this works for you!