he minimum number of customers and the maximum number of ISVs in the context of telecom billing mediation software. This software is responsible for gathering raw data describing service Vertical Integration due to Small Market Size and High Product Development usage, aggregating this data and converting it into billing statistics. The raw data is collected by collectors/adapters each targeting a specific type of network elements (controllers, routers, switches, transceivers, etc.); the collected data is aggregated and processed by the mediation software, and the results are delivered to a billing system (BS). Besides BS, also fraud, revenue assurance, dataware, interconnect etc. systems may be the recipients of the information. In order to assess the minimum number of customers needed, the ratios C C2, and m/Cinit have been estimated by consulting the Dittberner's OSS/BSS KnowledgeBase, and by interviewing OSS/BSS domain experts. According to the information obtained, the ratios take the following values: C1 22 0.2, C2 22 0.1, and m/Cinit 22 3. The cost of developing for reuse is 1.5-2 times greater than the cost of developing a non-reusable equivalent (Poulin et al. 1993; Frakes and Terry 1996); therefore, p is assigned the value of 1.75. Then, the boundary condition for the number of customers can be estimated: ==14.07. Thus, a vendor of telecom billing mediation software should have at least 14 operators as its customers. Given approximately 650 CSPs globally, the maximum number of software product vendors in this market segment is 650/14-46. This is quite close to the information provided by the Dittberner's OSS/BSS Knowledge- Base for 2006, wherein 42 software vendors offering mediation software are reported. The business processes automated by the software in the higher layers of the OSS/BSS software (i.e., CRM and Service software layers) are closer to the end-customers and are less technology-specific or telecom-specific. These process- es may have similarities with processes in other industries, and the