Future heterogeneous wireless networks will encompass different link layer technologies and allow selecting the most appropriate network depending on different criteria. To support mobile nodes in the selection process, network information services are developed that provide the mobile node with sufficient information about its network neighborhood, typically focusing on the optimization of handover processes. In this paper, we take a more general approach towards network information services, which is needed to support mobile communications in the existing environments of WLAN hotspots and wide area mobile communications networks. We introduce the notion of "service maps", a mobile data management approach allowing a mobile user to obtain a detailed view of available networks and the services they offer depending on the user context such as geographic position, mobility paths, and application requirements. We review our experiences with networking in highly mobile scenarios from which we derive a set of requirements for a general information service and present our system design and data model that also accounts for business and (incremental) deployment considerations