I came across this relic during a brief stop along the A3 Autobahn driving home frome Switzerland earlier this week. I almost overlooked it completely, as you ignore so much street furniture and loud advertising you come across. Only on second glance it registered as a public telephone.
Public phone, at the Siegburg-Ost Raststätte along the A3 near Köln. A relic in an open air museum almost.