Rising complexity of international IT projects has compelled service providers to re-define their customer-service approach. This paper uses a case study method to identify critical success factors for customer interaction as IT service providers run projects to deliver services to intrafirm end-users. Our analysis found that process-level, social and psychological factors were decisive in promoting successful provider-customer relationships. Three major factors - knowledge of the customer’s business and it’s need of IT-support, a close project collaboration and trustful, clear, understandable communication - are the cornerstone of successful IT service practices when coupled with a clear customer-oriented value proposition. Therefore, we identified the “bridgehead”-concept as an effective method to close a lack of understanding between business and IT. Our results suggest that both the provider and customer benefit from a close and iterative calibration of needs and services, with a high level of transparency, to ensure process efficiency and customer satisfaction.