Mobile devices such as Personal Digital Assistants (PDAs) or smart phones are rapidly increasing their graphics and networking capabilities. However, real-time rendering of large terrains is still a challenging task to accomplish in such limited devices. In this paper we describe the principles involved in the design and development of a scalable client-server architecture for hybrid rendering of terrains over wireless networks on mobile devices. We have developed a hybrid adaptive streaming and rendering method based on a server-client approach. The rendering workload is distributed between a server and the clients and the terrain is partitioned into the close-range geometry and the background. The close-range geometry is downloaded from the database and rendered on the mobile client, and the background is portrayed as a view-dependent panoramic impostor and rendered by the server on demand then it is sent on request to the server for display. The system architecture is organized in three levels: the main server, the panorama server and the mobile device client. This architecture provides support for efficient delivery of geometry and impostors to mobile clients according to their capabilities. As a proof of concept, we have implemented a prototype and carried out exhaustive experiments considering different network scenarios and different number of connected clients. The analysis of the server workload and response times shows that our architecture achieves a great scalability and performance even when using low-end mobile devices.