We present an application of software model checking to the analysis of a large industrial software product: Lucent Technologies' CDMA call-processing library. This software is deployed on thousands of base stations in wireless networks world-wide, where it sets up and manages millions of calls to and from mobile devices everyday. Our analysis of this software was carried out using VeriSoft, a tool developed at Bell Laboratories that implements model-checking algorithms for systematically testing concurrent reactive software.VeriSoft has now been used for over a year for analyzing several releases and versions of the CDMA call-processing software. Although we started this work with a fairly robust version of the software, the application of model checking exposed several problems that had escaped traditional testing. Model checking also helped developers maintain a high degree of confidence in the library as it evolved through its many releases and versions.To our knowledge, software model checking has rarely been applied to software systems of this scale. In this paper, we describe our experience in applying this technology in an industrial environment.