The widespread deployment of wired and wireless networks in both horizontal and vertical overlays presents new opportunities and challenges for developers of services. Users of these networks have multiple end devices, some of which are mobile, which complicates (and sometimes prevents) the transparent use of services across the networks. This paper presents an architecture for enabling the dynamic handoff of active services across multiple networks (cascaded networks). The architecture supports the rapid development of innovative new services and enables the use of serviceand user-specific policies for transcoding and routing information between networks. These policies allow services to determine the "best" mode and route to use in reaching a particular user. The architecture described in this paper is being built on top of a campus-wide testbed consisting of GSM digital cellular, wireless and wired IP, and public switched telephone networks. An example application has been constructed to demonstrate the utility of the architecture.