We present a five phases approach for the cost-efficient design of communication platforms. We start with complete and executable models of the system function that capture all essential parts of a reference application, i.e. processing kernels, data and control flow, and timing constraints. We analyze such an architectureindependent model to narrow the design space and derive a most flexible initial platform architecture. We map the model onto the platform hardand software, and profile the system. Through iterations, the prototype is refined, until an architecture is found that meets performance and cost constraints. The resulting virtual prototype serves as executable specification for the design of the final system. Two case studies from wireless communications (Software Defined Radio, SDR) and access networks (Digital Subscriber Line Access Multiplexer, DSLAM) illustrate our approach.