We present a novel middleware approach for invehicle service discovery and device integration that is based on the concept of Service-oriented Architectures (SOA). In order to be able to identify a suitable SOA system, we define a series of criteria the SOA platform should fulfill. These criteria take into account the specific requirements of the automotive domain. Based on these criteria we compare nine different SOA standards and show why the Device Profile for Web Services (DPWS) standard is most suitable as the middleware of an in-car infotainment and communication system. Furthermore, we present a prototypical implementation of an in-vehicle network based on the DPWS middleware. Hence, we enable the integration of nomadic devices by providing their functionalities within the network and consequently including their graphical output into the in-vehicle Human Machine Interface (HMI). Due to the system design it is also possible to use nomadic devices as an additional display to present the HMI. Finally, an in-vehicle controller is included into our SOA and therefore available to all other devices within our system.