Nowadays, telecom software applications are expected to run on a tremendous variety of execution environments. For example, network connection software must deliver the same functionalities on distinct physical platforms, which themselves run several distinct operating systems, with various applications and physical devices. Testing those applications is challenging as it is simply impossible to consider every possible environment configuration. This paper reports on an industrial case study called BIEW (Business and Internet EveryWhere) where the combinatorial explosion of environment configurations has been tackled with a dedicated and original methodology devised by KEREVAL, a french SME focusing on software testing services. The proposed solution samples a subset of configurations to be tested, based on environment modelling, requirement analysis and systematic traceability. From the experience on this case study, we outline the challenges to develop means to select relevant environment configurations from variability modelling and requirement analysis in the testing processes of telecom software.