Service-oriented architectures (SOA) aim at the alignment of business and IT by having a clear business process-centric focus. In order to reach that goal, real-world business processes are captured by business process models. These models serve as the basis for the declarative configuration of a SOA using appropriate deployment artifacts - i.e., XML-based process languages. Consequently, requirements engineering for SOAs must focus on business processes and on their integration into systems using interoperable services, which is not the case for most conventional requirements engineering approaches. In this paper we present a requirements engineering approach specifically designed for the engineering of SOAs. Requirements are captured using a unified process, based on phases and iterations eventually leading to a formalized and unambiguous requirements specification. The final requirements specification can be used in succeeding development phases - i.e. for the model-driven generation of deployment artifacts for SOAs. The presented solution is called [vem:xi:] and is successfully used in the IT department of a Mobile Network Operator (MNO) in Austria. In the highly volatile world of mobile communication the presented approach enables faster application development and faster integration of solutions, thus leading to a competitive advantage over other market participants.