 increase in the system modularity value after the integration, the greater is the improvement in hiding complexity and creating innovation potential, and hence the more likely the integration scenario is. It is noteworthy that subsys- tem interconnectivity and modularity may affect the process of vertical disintegra- tion of the software: if a vertical integration gives a better system modularity, as compared to the horizontal integration, the process of vertical disintegration may be hindered. In order to get an insight to how the system modularity affects the OSS/BSS software, we use a TMForum's technical program, called the OSS through Java (OSS/J) initiative, which develops application programming interfaces (APIs) aligned with the TMForum's NGOSS framework. In the frame of OSS/J, a roadmap Vertical Integration due to Software Systems' Modularity of APIs is elaborated, and for each OSS/BSS application area, a software specifica- tion, a reference implementation, and a technology compatibility kit is provided. In the software API specification and implementation roadmap documents, the APIs to be implemented are listed, and their dependencies are illustrated (OSS/J Product Team 2006). These dependencies are used below in order to compare different scenarios of integrating OSS/BSS software subsystems. The scenarios to be compared are derived from the operations process areas specified in TMForum's eTOM. Within the operations process area, eTOM distinguishes four vertical process groupings (Fulfillment, Assurance, Billing, and Operations Support and Readiness (OS&R)) and three horizontal process groupings (Customer Relationship Management (CRM), Service Management and Operations (SM&O), and Resource Management and Operations (RM&O). Therefore, the following seven integration scenarios are compared: Vertical integration of Fulfillment software Vertical integration of Assurance software Vertical integration of Billing software Vertical integration of OSR software Horizontal integration of CRM software Horizontal i