In iCal on your Mac, only the URLs that start with "http://" in the field you map to the "URL" field in SeedCode_Subscribe_Setup.fmp12 will appear as clickable links that open in your default browser. URLs in any other fields (e.g., the "Description" field) will not be clickable in iCal.
In iOS, URLs in any field will open in Safari, and addresses will open in Maps. And if you click on a phone number in any field, your iPhone will offer to call that number.
But I Want More!
No problem! Make a calculation field in your database that concatenates the contents of multiple fields (maybe using the List function), then designate that field as the "Description" in SeedCode_Subscribe_Setup.fmp12. You can include lots of information on your calendar event this way, and all of the link-types mentioned above will be clickable. Cool!