In-car navigation systems are increasingly evolving into powerful mobility assistants which, in addition to conventional functions such as routing and providing directions, can offer the driver manifold information resources and services. Through this, they will also become an important supportive technology for making mobility with electric vehicles more effective and acceptable. More intelligent methods of trip planning and routing will be required for e-cars due to the current constraints concerning charging time and availability of charging stations. Moreover, by flexibly integrating different information resources and services available on the Internet, trips can be better aligned with the driver's tasks and needs, opening up opportunities for new business models for service providers and merchants. Primary methods for integrating heterogeneous services in a smart mobility assistant are provided by Semantic Web technologies and standards. This article discusses the different requirements for a mobility assistant, describes the underlying technologies, and presents a prototypical system that was developed in the colognE-mobil project.