Voice communications apparatus is connected to a general subscriber telephone set or a broadband telephone set, to communicate over the public switched telephone network. The apparatus includes a filter converting signals such as to satisfy signal conditions prescribed for the telephone network. The apparatus also includes a terminal class determiner for determining the class of the telephone set connected, and a circuit for changing at least the sampling frequency at which the analog signals from the telephone set are sampled. This establishes high quality in broadband voice communications. The terminal class determiner may automatically determine the class of the telephone set at any timing of a call sequence by detecting a band component of the signals from the telephone set, a predetermined frequency of a signal intermittently transmitted from the telephone set or the characteristics of the telephone set.