"iCalendar, defined in the IETF's RFC 2455, is supported by Outlook, Apple's
iCal®, Mozilla Sunbird, and several other calendar applications."
Interoperability problems persist. As a security measure, my copy of Outlook is not configured to send mail, only to receive it. (I use other mail programs to send, and receive Outlook mail only in limited circumstances.) But Outlook 2002's inability to open an .ics file is indicative that there are still interoperability problems. And ultimately, I need to be able to sync my Pocket PC with any mail client or service, not just with Outlook.