Wood desk phone: an early telephone device used both as transmitter and receiver. It is accompanied by a wire connected to a telephone inverter or telephone exchange breadboard. It was one of the first "pestle-type" telephones used by the German Post Office service, initially, for connecting telephones with an existing telegraph network. In 1891, it became so useful that Siemens had to adjust a special coin receiver on the device to make access to telephony more widespread. Since Graham Bell had not patented the invention of telephone in Germany, Siemens&Halske company managed to expand its telephone network -on the basis of this device- and patented it in December 1877, in Germany.