This article, a contribution to the analysis of service relations, draws on an ethnographic study of reactions to faulty lines at a major French telecommunications operator. Focused on the situation of mutual engagement of agent and user in the technical activity, it shows the affordances on which agents and users take the risk of relying in the game of cooperation. The author concludes that the relationship itself, at once production of an agreement and delivery of a service, is always based on a technical relation.