This article explains how to setup an Exchange ActiveSync account on your iPhone, iPad or iPod touch.
Contact your Exchange Server administrator if you are unsure of any of the required information
Tap Settings > Mail, Contacts, Calendars > Add Account > Microsoft Exchange.
Enter the information in the fields above, then hit Next:
-Email: your email address.
-Domain: not required.
-Username: your email address.
Your iOS device will now try to locate your Exchange Server. If necessary, you will need to enter your front-end Exchange Server's complete address (owa.mailhost123.com) in the Server field.
Choose which content you would like to synchronize: Mail, Contacts, and Calendars. Tap Save when finished.
Note: To modify your exchange settings, Tap Settings > Mail, Contacts, Calendars, select your Exchange account, and tap Account Info.