ISDNCLID identifies a phone number via the Calling Line Identification Presentation feature of ISDN lines and presents the number on the screen. It keeps a log of the received calls, so the last time that the same number has called, is shown, too. The program has a phone book, so phone numbers can be directly converted in names.

For italian users, the program accesses white-pages on the web and shows all the data present on the web for the calling number.