Seamless service provisioning strongly depends on Vertical HandOff (VHO) as key technology that is especially indispensable for the successful management of emergency operations. Latest mobility solutions, including vertical handoff decision algorithms and executions, are related to high technical and economic costs preventing the immediate introduction of VHO technologies. In order to benefit at an earlier stage from seamless emergency services, we present a holistic cost-effective Client based Secure Handoff for Mobile Units (CSH-MU) solution combined with an energy-efficient Vertical Handoff Decision Algorithm (VHDA) that considers the limited system resources of mobile phones (e.g., restricted access to decision metrics, battery life). For performance evaluation and as proof of concept, we develop a comprehensive simulation model and a real experimental test bed to analyze the gain of our energy-efficient decision algorithm for TCP and UDP based applications. For this purpose, the developed energy model is derived from real measurements based on a mobile phone. Confirmed by the results, using the proposed VHDA with energy model enhances the performance in terms of higher throughput and lower power consumption.