Bellcore has developed a model to support the periodic calculation and reporting of customer costs resulting from poor quality in telecommunications switching system software. This model is designed to provide, as a primary output, total switching system software cost of poor quality, along with a breakdown of this total by major cost component. The primary input to the model is software RQMS data, described in Bellcore's reliability and qualify measurements for telecommunications systems, TR-TSY-000929, and reported by switching system suppliers to the divested Bell operating companies (telcos) on systems operated by these companies. Telco and switching system supplier alike are expected to benefit from the ongoing application of the model, through which accumulated maintenance cost information will be made available to support telco switching system management functions and supplier quality improvement efforts.>