n network interface. Thus, in order to enter and compete in the OSS market or its segments, a vendor must possess knowledge on vertical processes and interfaces. In Fig. 5, depicting the evolution of a vertical software market where the share of primary software industry from the total volume increases gradually, the different motivations for mergers and acquisitions are shown connected to the evolution phase. The main reasons for acquisitions in the initial two phases and in the transitional third phases are likely to be associated to acquiring resources for knowledge and capacity as well as customer relationships. In the last phase, the saturated market drives cost reductions, which are the likely reasons for mergers. 4.2 Analysis of the Impact of M&A Activities in the OSS Market The model describing the emergence of a vertical software market also embodies the change of degree of horizontalization through standardization. In the earlier phases, the vendors providing software products are missing as the manufacturing of products for the industry is not possible. Later, standardization enables software product to appear and to be sold across industries. In the context of the telecom- munications software industry, an example of the horizontalization in the earlier phase would be software vendors' ability to provide mediator software for two or more customers. Horizontalization across technologies occurred later when, e.g., the same customer relationship management (CRM) software was provided both for mobile and broadband networks. CRM software is also a good example of cross- industry horizontalization in that the same product may be provided for both telecom and financial industries by a single vendor. In order to investigate the impact of M&A activities on the horizontalization in the telecom software market, we first assumed that company acquires resources, knowledge and customer relationships to enter the market, strengthen its position in one segment or to provide new product to a new segment within the mar