Granting write permission for calendar sharing with OWA 2010
The calendar sharing feature introduced in Outlook Web App 2010 (OWA) allows a user to grant access to their calendar to another user. To access the option, click on the Share option when in the Calendar and then on Share This Calendar. You’ll then be able to select the user(s) that you want to share your calendar with and define the level of information you want the recipient to be able to see in your calendar.