The iPhone user can add the calender from webmail into the device by using the CalDav funtion as guideline below:

1. Open the settings application
2. Tap Mail, Contacts, Calendars
3. Tap Add Account

4. Tap Other as account type
5. Tap Add CalDAV account

6. For server, type mail.yourdomain.com
7. Enter your full email address for User Name, and then type your password.
8. If your mail server does not support SSL, a warning will be displayed. Tap Continue and disable the SSL.
9. Your calendar will now be visible in the Calendar application.