The ZB SA 24 was developed by Siemens & Halske for the Deutsche Reichspost as a standard desk telephone. It was produced by many other makers under licence in many variants.
ZB SA stands for Zentralbatterie-Betrieb/Selbstanschluss-Betrieb and 24 refers to the year of introduction, 1924.
It was developed from the somewhat larger ZB SA 19.
The ZB SA 24 has a high antler like hookswitch assembly, to accomodate a trumpet shaped speaking tube on the handset. This model was equiped with many different kinds of handsets and rotary dials. The two examples here have a so called pepperpot mouthpiece on the handset and neither of them has a Siemens & Halske dial.
The upper telephone is a normal desk Phone with a TEFAG dial. The lower Phone is a two line office phone. A line was selected by pressing the white or the red button on top. This telephone has a Fuld dial.