3D maps can visualize static and dynamic features of real environments, and act as 3D gateways to location-based information. Insufficient network speed has been a major bottleneck for dynamic download of 3D content for mobile devices. 3G network technologies promise to solve this issue, allowing faster response times and higher data rates. Similarly, mobile 3D graphics hardware should provide a dramatic increase in rendering speed. We examine wireless IP network properties, and develop an optimized network scheme suited for navigation purposes. The presented system allows free roaming in the 3D scene, while progressively down-loading 3D data. For case platforms, we use two 3G Symbian smart phones, one with 3D hardware and one without. Network, 3D rendering and overall application performances are measured. For a scalable 3D engine, 3D hardware improves the rendering performance by over an order of magnitude. By using a compressed network protocol and efficiently formatted 3D data, a textured but lightweight 3D city can be progressively downloaded in 3G networks fast and without degrading application responsiveness.