Name: Your Name (What ever you want)
Email: Your email address is your username
Password: Your att.net account password
Description:
Click Next Button
Hostname: imap.mail.att.net
Username: Your email address is your username
Password: Your att.net account password
Hostname: smtp.mail.att.net
Username: Your email address is your username
Password: Your att.net account password
Click Save Button
Use SSL: Yes
Authentication: Password
Server Port: 993
Use SSL: Yes
Authentication: Password
Server Port: 465
You can login att.net and Signup for att.net new account on your iPhone from here.