This article proposes an approach for improving the software process of a small/medium company. The methodology is presented through a case study during which estimation models have been applied, evaluated and introduced in a telecommunication software development process. The proposed methodology uses Bayesian Belief Networks to represent the relationships among implementation, product and process metrics and their impact on the development effort. The estimation models that were derived were applied and evaluated on the on‐going projects of the company. Finally, by performing the same analysis on data from the International Software Benchmarking Standards Group (ISBSG) repository, it is demonstrated how one company can utilize data from other companies when it lacks sufficient data of its own. Copyright © 2009 John Wiley & Sons, Ltd.