I'll be going to ZKM next week. From the photo ( http://hop3.de/mobiltelefon_en.html ) it seems like the phone displays the number of missed calls. I'll let you know what it says.
As anotheryou said, the phone is sadly limited to displaying double-digit numbers of missed calls. It did ring every couple of minutes though while we were there. We were playing with the idea of calling the people back (like any phone it shows the caller's number unless the caller chooses to prevent that) but in the end we didn't.
