The advent of the cooperating IP-enabled heterogeneous radio networks will offer, under the “Beyond 3G” vision, ubiquitous services. In this new challenging context, a novel architecture has been designed within the control plane to avoid modification of existing networks. Therefore, a new entity in the network, a complementary middleware in the terminal, and enhanced signaling protocols were introduced. In order to prove the deployment feasibility of this solution, a testbed has also been implemented to demonstrate service signaling, discovery and management concepts in such a heterogeneous environment. This paper presents different functionalities and components that have been prototyped in this “Beyond 3G” demonstrator, as well as our experience in building such a complex testbed.