This chapter deals with the application of automatic speaker classification in human machine dialog systems based on telephone operation. In a first step we introduce a taxonomy based on three features that such systems might have. We explain the features, namely online, mirroring, critical and their respective counterparts get explicated and are than used to characterize a part of the exemplary applications that illustrate the benefit of that approach. Furthermore prototypical application scenarios are described that shall illustrate the vast possibilities to utilize automated speaker classification in dialog applications.