A selective call communication system (100) has a speech recognition system using an acoustic space (400) which has a plurality of probability density functions (pdfs). The selective call communication system (100) has an acoustic space generator (136) for representing speech in the acoustic space (400) which has a plurality of regions (1-14) having a subset of the plurality of probability density functions (502-516). The selective call communication system (100) has a tree generator (138) for generating a hierarchical tree structure (500) representing the subset of the plurality of probability density functions (502-516) associated with the plurality of regions (1-14), a score computer (132) for determining a region of the plurality of regions (1-14) indicative of a minimum distance to a center of the region for a speech sample received, and a speech recognizer (130) for calculating the probability density functions of the region for recognizing the speech sample received.