Museum für Kommunikation is one of the stronger stops on Frankfurt's museum embankment, especially if you like the everyday history of how people keep in touch. The exhibits move from postal routes and telegraphs through telephones, fax machines, and the internet, with enough working displays to keep it from feeling like a cabinet of old devices.
Descriptions are in German and English, and the interactive sections make it a good choice with children. Leave a little time for the temporary exhibitions and the small art collection, which picks up communication as a theme rather than treating the subject only as technology.