Apparatus that allows a called party, while engaged in a first call, to indicate to a second calling party that he/she is aware of the second call and will respond to the second call within a waiting time interval. The second calling party is given a "personal answer" message indicating that the called...http://www.google.de/patents/US5034975?utm_source=gb-gplus-sharePatent US5034975 - Voice announcement device for improving functionality of multi-line telephones
