IMAP settings. This works for @sbcglobal.net. Probably works with any other AT&T domain that is hosted with Yahoo.
To set up Internet Message Access Protocol (IMAP) on your mobile device, please use the following settings:
Incoming Server - imap.mail.yahoo.com
Outgoing Server - smtp.mail.yahoo.com
Incoming Port - 993 (requires SSL)
Outgoing Port - 465 (requires SSL/TLS)
User name: full email address (for example, firstname.lastname@example.org or email@example.com)
Password: the password you log in to Yahoo! with.