Frishauf, Holtz, Goodman & Woodward
Key telephone system with means for operatively connecting another key telephone systems
 A key telephone system comprising a main equipment and a plurality of key telephones connected to the main equipment and comprising elements for operatively connecting another similar key telephone system. The main equipment in the key telephone system comprises a system call transmitting interface and a system call receiving interface which are connected through connecting lines to a system call receiving interface and a system call transmitting interface in a main equipment of another similar key telephone system, respectively. Each key telephone in both systems comprises an additional key for selecting the system call transmitting interface of its own main equipment. By use of the additional key in one key telephone, a speech path can be established between the one key telephone and another key telephone in another key telephone system through both main equipments and the connecting line. By operation of the additional key after operation of a holding key of a key telephone in a key telephone system, an office line call to the key telephone is transferred to a key telephone in the other key telephone system through the connecting line. 
Nitsuko Limited Nippon Telegraph and Telephone Corporation
H
H04M
inventional
Yoshiji Jouji Tetunobu Minoru
Tanimoto Tanaka Watanabe Okumura