• In your iPhone, click on Settings
• Click on Mail, Contacts, Calendars
• Click on Add Account
• Click on Other
• Enter your Name, Address e.g. yourname@king.net, Password, Description ex. IMAP Email Sample
• Save your configuration
• Go back to Mail, Contacts, Calendars and select the IMAP Email Sample. This will show the IMAP Account Information e.g. your Name, Address and Description.
• Incoming Mail Server, update your Host Name ex. mail.king.net, Username ex. kingnet/yourname; kingnet is your network domain name and your Password
• Outgoing Mail Server, SMTP is cwmx.com. Please note if you can't send out email. Please call AT&T Customer Service to let them know that you're having issue sending out using IMAP through cwmx.com SMTP Server.
• Save and Exit

Now check your mail and you should see new messages start downloading.

Useful links to secure IMAP:

• http://www.tacteam.net/isaserverorg/exchangekit/2003secureimap4/2003secureimap4.htm
• http://nobodywantsastyl.us/2007/08/if_imaps_isnt_secure_enough_wh.html

Don't hesitate to post your question here.