We present a synchronous framework for modeling, specifying telephone systems, and detecting interactions among services. The detection process is based on automated testing techniques provided by the tool that we developed, Lutess. Lutess allows its user to drive the test with operational profiles or behavioral patterns. The use of Lutess in the First Interaction Detection Contest led to very good results, since most interactions foreseen by the Contest Committee were detected. 1 Introduction This paper is concerned with the use of formal description techniques for the detection of telephone feature interactions, at the specification stage. It focuses on our proposal for detecting interactions in the First Feature Interaction Detection Contest, held during the Fifth Feature Interaction Workshop [12]. A feature interaction occurs when the activation of two features (or two activations of the same feature) produces an unexpected behavior. Although much effort has been devoted to this...