As the International Space Station is the largest object in a low orbit around the Earth, it can easily seen with the naked eye at dusk or dawn. There have been several successful attempts to use it as a reflector for radio waves to complete amateur radio QSOs on 2m and 23 cm.
Summary of related entries in chronological order:
ISS Bounce V: The QSO! (including audio files)
The full story of the first QSO can be found in CQ DL issue 2013/08, page 583-584 (in German). More publications: Here