rket evolution model) that the software product vendors supporting only a limited set of network interfaces dominate the OSS/BSS market segments in the later phases. Indeed, large vendors are oriented towards IT services and have a stronger role in the market segments which are in the earlier phase of the software market evolution. These companies provide mainly professional services and have more resources and are capable to support the telecom operators who are compromised to maintain a broad variety of legacy network technologies in the earlier phases of the market evolution. We verified, also at the level of individual companies, the negative correlation of the product orientation (the percentage of revenue coming from software product licenses) and the company size with a data set of 198 OSS software vendors. The OSS software revenue from telecom operators is negatively correlated with the share of revenue from product licenses at a statistically significant level (Spearman's rho of 0.281**). This is also in line with the whole product model, wherein the service content of the whole product decreases until the fully integrated and commoditized whole product is reached in the late majority phase. Analyzing the Current Phase of the OSS/BSS Software Market These results suggest that the split of software spending into (1) in-house development, (2) professional IT services, and (3) software licenses can be consid- ered as an indicator for technology diffusion and as an indicator for a phase of vertical software market evolution. It was further concluded that the market seg- ments within a single industry could be in different phases of evolution, although they might follow a similar development trend. OSS/BSS Software Market Evolution Through M&A The operations support systems constitute a $30 billion vertical market for software vendors and system integrators. On one hand, the market is gradually maturing (see Sect. 2 in chapter on, "Analyzing the Current Phase of the OSS/BSS Software Market" and Frank and Luom