The options to share, or publish calendars using the iCal format are available to end users via Outlook Web App or via Microsoft Outlook 2010. In reality, both use the same interface to configure publishing options; however, accessing these options differs between Outlook Web App and Outlook 2010.
To publish a calendar for sharing with iOS devices in Outlook Web App, log in as normal and navigate to the calendar.
Above the main calendar displayed, the option to Share should be available as a drop down menu. Click Share, and then choose Publish this Calendar to the Internet:
Next, configure the relevant settings that the person or people who should have access to the calendar should see, along with an appropriate access level. Pay particular attention to the access level, as this is the setting that defines whether the calendar is public or "restricted". A public calendar can be discovered by any entity that knows the username...