The new services and applications that can rise in the upcoming years will be the multi-network systems integrating next generation and traditional networks. Those services and applications will guarantee transition and compatibility between different generations of network systems. Within this dissertation we focus on conferencing applications in Mobile Ad hoc NETworks (MANETs) and Multihop Cellular Networks. Conferencing includes popular applications such as audio/video conferencing and massive gaming. It requires two sessions: a call signaling and a media handling. Call signaling is used to set up conference sessions. Media handling deals with aspects such as media transportation and media mixing. We propose a self-organizing media handling architecture based on two overlay networks: one for mixing and one for control. For mixing, a distributed mixing architecture that balances the load among the nodes according to their capabilities is proposed. The control tasks are assured by a media signaling protocol based on an extended version of Megaco/H.248. For Multihop Cellular Networks, media mediators are used to connect the entities of MANETs with the entities of Cellular Networks.