There is only one file type that uses the .ULS extension:
NetMeeting User Location Service File
Contains information about an Internet location; used by Microsoft NetMeeting to connect users to each other; the Internet Locator Server (ILS) sends a file called "Ulserver.uls" to clients with IP address and port information.
NetMeeting was part of Windows XP, but is not included with Windows Vista. It has been replaced by Windows Meeting Space and Microsoft Office Live Meeting.
Updated: June 14, 2008