The 3GPP IP Multimedia Subsystem (IMS) is currently expected to provide the basic architecture framework for the Next Generation Network which will bridge the traditional divide between circuit-switched and packet-switched networks and consolidate both sides into one single network for all services. Therefore, the imminent commercial roll-out of IMS will have immense impact on the whole way future mobile business applications are designed, developed and deployed. This paper presents a survey about the application-oriented research project CAMPARI (Configuration, Architecture, Migration, Performance Analysis and Requirements of 3G IMS) which aims at inves-tigating a "minimal-optimal" IMS configuration with respect to architecture and Quality-of-Service aspects. After a brief survey of the IMS core components, we introduce our OpenSER-based IMS prototype implementation and pre-sent the "IMS in a bottle" approach. Based on our practical experiences with this testbed system, we finally discuss important current and future challenges including migration, interworking, charging, identity management, security, and regulatory aspects.