According the present invention, a line using status of each personal station which contains an existing analog line in a route between the personal station and an exchange unit is determined. The PS number of a personal station having a telephone call, the line number used for the telephone call, and...http://www.google.de/patents/US6333977?utm_source=gb-gplus-sharePatent US6333977 - Communication method authenticating a personal station and calculating a fee of a telephone call from the personal station
