iCalendar files are based on the set of data exchange specifications which also includes vCards. You may come across them either in emails or from a website. For example some sites which sell travel tickets allow you to download your itinerary in an iCalendar file. While Windows Phone has always supported vCards for contact information it doesn’t recognise iCal files.
Since Windows Phone 8 introduced the ability to register for file associations this allowed me to use some old code I wrote back in the days of Pocket Outlook on Windows CE and Windows Mobile. My free iCalendar Import application has just become available in the Store for Windows Phone 8. You can download it from the link below. I’d welcome any feedback. There are some limitations on the supported event types – there is no way to insert recurring appointments into the user’s calendar so this supports single events only.