Both Microsoft Exchange on-premise and the hosted version of Office 365 provide a calendar publishing feature that makes it easy to share your calendar free/busy information with your friends and family.

For end-users, it takes less than 5 minutes to have this working and only takes a few mouse clicks.

1. Logon to Outlook Web Access and click on the Calendar.

2. Click on the Share menu, and then click on “Publish this Calendar to Internet’

3. Select the Publishing detail (how much do you want to share, the full details of your calendar or just when you are free or busy? Also, select the access level – should anyone be able to view your calendar or only those who receive a link to your calendar?

4. That’s it! Now, to share your calendar, just click on the Share Menu again, and select  ‘Send Links to This Calendar.

5. Enter the email address of your friends or family

After you click Send, then the recipient/s will get an email with an invite. When they click on the hyperlink containing the .ics file, they will have a pop-up message like the one below ‘subscribe to the calendar?’

After they click Subscribe, they will then be able to View your calendar.

The previous steps just work out of box with Office 365. However, if you do not have Office 365, your email administrator can still setup Internet Calendar Publishing if they are running Exchange 2010 SP1 or later. For more information, see:
http://technet.microsoft.com/en-us/library/ff607475(v=exchg.141).aspx