The ever-increasing heterogeneous network infrastructure offers mobile users access to a variety of information and entertainment services. To enhance the user experience and the availability of these services, it is mandatory that Internet services have to be provided without interruptions via heterogeneous networks. This implies the development of a method that enables seamless switching (Vertical Handoff) between different wireless network technologies (e.g., UMTS, WiFi). In addition, Single Sign-On (SSO) systems are required to enable fast and secure access with minimal interaction to geographically distributed services.Given these requirements, this thesis presents novel network operator independent handoff solutions for seamless data and voice communication. Furthermore, a new federation concept with single sign-on feature is proposed that allows secure interoperability of heterogeneous information services for fast service access and higher user experience. The solution concepts developed in this thesis target an entire operational spectrum of the user application environment for seamless service provisioning.The challenging requirements are derived from joint research projects with different rescue organizations where vertical handoff and single sign-on solutions support efficient emergency process management in large-scale emergency events.The performance evaluation of the proposed solutions in this thesis has been performed by experimental test beds, simulation and analytical methods. The results illustrate that the solutions have not only a significantly higher performance (e.g., short delay and response times), but also a lower integration effort in comparison to existing standard approaches.