, for a majority of CSPs, the spending on externally acquired software exceeds considerably the spending on the internally developed software and is typically even up to ~3 times higher than internal spending. Meanwhile, for a handful of CSPs (AT&T, BT Group, Telstra, KT Corp., and Taiwan Mobile) considered here, the spending on internal software prevails. Most of these CSPs are large incumbent telecom operators that evolved from former large state (BT, Telstra, KT) or national (AT&T) telecom operators, often monopolies. Due to their historical development, they have a highly complex unique large-scale infrastructure accumulated over decades of operations, and no independent Analyzing the Current Phase of the OSS/BSS Software Market Mean = 1.09 Mean = 1.92 Std. Dev. = 1.864 Std. Dev. = 4.439 Ratio of internal to external software spending 2007 Ratio of internal to external software spending 2006 Mean = 1.02 Std. Dev. = 1.974 Ratio of internal to external software spending 2005 Fig. 2 Distribution of the ratio of internal to external software spending software vendor has sufficient knowledge and experience to implement and main- tain the required software. It is noteworthy that, according to the Dittberner OSS/BSS knowledgebase, the internal software spending by the CPSs exceeds the external software acquisition. The discrepancy may be attributed to the fact that the Dittberner database better represents US-based CSPs, where internal software development is more common than in the rest of the world. The ratio of internal/external software spending differs in different phases of software market evolution, and it can therefore be also seen as an indicator of the evolution phase. Using the Dittberner database, the relationship between the product-related and bespoken software development were approximated (see below). The product-related expenses include product license, product-related services, and integration. The bespoken software development includes only L. Frank et al. Table 8 Share of CSP's Min (%) Max (%) Av