This article reports on a case study performed in cooperation with a telecommunication provider. The telecom business changes rapidly as new services are continuously introduced. The rapidly changing business environment demands that the company has supportive flexible software. The company’s continuous evolution of the IT-infrastructure makes it necessary to tailor the interaction between different applications. The objective of the case study was to explore what is required to allow end-users to tailor the interaction between flexible applications in an evolving IT-infrastructure. The case study followed a design research paradigm where a prototype was created and evaluated from a use perspective. The overall result shows that allowing end-users to tailor the interaction between flexible applications in an evolving IT infrastructure relies on, among other things, an organization that allows cooperation between users and developers that supports both evolution and tailoring.