The right superior temporal sulcus (STS) is involved in processing the human voice. In this paper, we report fMRI findings showing that segregated cortical regions along the STS are involved in distinct aspects of voice processing and that they functionally cooperate during speaker recognition. Subjects listened to identical sets of auditory sentences while recognizing either a target sentence irrespective of the speaking voice or a target voice irrespective of the sentence meaning. As the same stimulus material was used in both conditions, task-related activations were not confounded by differences in speech acoustic features. Half of the stimuli were voices of familiar persons and half of persons that were never encountered before. Recognizing voices activated the right anterior and posterior STS more than recognizing verbal content. While the right anterior STS responded equally to both voice categories, the right posterior STS displayed stronger responses to non-familiar than to familiar speakers' voices. It also responded to our baseline condition of amplitude modulated noises that required a detailed analysis of complex temporal patterns. Analyses of connectivity (psychophysiological interactions) revealed that during speaker recognition both anterior and posterior right STS interacted with a region in the mid/anterior part of the right STS, a region that has been implicated in processing the acoustic properties of voices. Moreover, the anterior and posterior STS displayed distinct connectivity patterns depending on familiarity. Our results thus distinguish three STS regions that process different properties of voices and interact in a specific manner depending on familiarity with the speaker.