From Arnold Rupp:
The phone in the picture is not made by Siemens but it's a phone from the 30�s by the German company MIX & GENEST. A lot of these phones were made later worldwide but most of them in Europe in the 40�s, 50�s and 60�s under license by companies like BELL Mfg. Co, Belgium, STANDARD ELECTRICA in Spain and Argentina and some more. All these companies belonged to the WESTERN ELECTRIC INTERNATIONAL GROUP or ITT.
Because of the shape of the ears on the cradle, I guess that the phone in the picture left the pressing mould in Argentina. If so, the attached wiring diagrams should correspond to this phone.