The International Telegraph Union (ITU), later renamed as the International Telecommunication Union, was founded on 1865-05-17. The ITU became a United Nations specialised agency in 1947. Following the 100th anniversary of the founding of the ITU on 1965-05-17, an annual World Telecommunication Day (WTD) was established, to be held on 17 May each year. The first WTD was held on 1969-05-17. In 2005, WTD was renamed World Information Society Day. An amateur radio station is operated from the ITU HQ in Geneva to mark WTD, using a callsign in the series 4U#ITU. The table below lists these callsigns.
| Year | Callsign | Note |
| 1965 | 4U1ITU, 4U2ITU, 4U3ITU, 4U4ITU, 4U5ITU, 4U6ITU | 100th anniversary of the founding of the ITU |
| 1969 | 4U7ITU | First World Telecommunication Day |
| 1970 | 4U7ITU | |
| 1971 | 4U3ITU | |
| 1972 | 4U4ITU | |
| 1973 | - | Apparently not QRV |
| 1974 | 4U6ITU | |
| 1975 | 4U7ITU | 110th anniversary of ITU |
| 1976 | 4U8ITU | |
| 1977 | 4U9ITU |
|
| 1978 | 4U0ITU, 4U1ITU | 10th World Telecommunication Day |
| 1979 | 4U1ITU | |
| 1980 | 4U5ITU | |
| 1981 | 4U6ITU | |
| 1982 | 4U7ITU | |
| 1983 | 4U8ITU | |
| 1984 | 4U9ITU |
|
| 1985 | 4U0ITU | 120th anniversary of ITU |
| 1986 | 4U1ITU | |
| 1987 | 4U2ITU | |
| 1988 | 4U3ITU | 20th World Telecommunication Day |
| 1989 | 4U4ITU | |
| 1990 | 4U5ITU | |
| 1991 | 4U6ITU | |
| 1992 | 4U7ITU | |
| 1993 | 4U8ITU | |
| 1994 | 4U9ITU | |
| 1995 | 4U0ITU | 130th anniversary of ITU |
| 1996 | 4U1ITU | |
| 1997 | 4U1ITU | |
| 1998 | 4U1ITU | 30th World Telecommunication Day |
| 1999 | 4U1ITU |
|
| 2000 | 4U1ITU |
|
| 2001 | 4U1ITU | |
| 2002 | 4U1ITU | |
| 2003 | 4U1ITU | |
| 2004 | 4U1ITU |
References
Wikipedia - International Telecommunication Union
Wikipedia - World Information Society Day