Various apps seem to do UriSpaceSquatting using this scheme:
MS netmeeting; see NM: How to Create a NetMeeting Hyperlink on a Web Page Microsoft Corporation, 1998-04-22
skype; see A Public Service Announcement Regarding ‘callto:’ URIs and Safari, John Gruber, 16 December 2005.
See also other UriSchemes, especially UriSchemes/tel , discussed in rfc2806, URLs for Telephone Calls.