This study describes realization of conversational multimedia services in mobile networks. Characteristics and types of multimedia services, technological conditions making their introduction possible and quality of service mechanisms in different networks are described. Since conversational multimedia services are enabled today in circuit switching domain of UMTS network by introduction of 3G-324M standard, its architecture, protocols and the main scenarios of connection setup in those networks are presented. Traffic characteristics analyse of the video calls service in the network of the operator the first offering 3G services in its country has been performed. Some of today’s main reasons of the improper (not correct) disconnection of the video calls are described and the actions the operator can take to solve them are pointed out. It is presented how packet networks can offer better efficiency and flexibility of the conversational multimedia services and the architecture, protocols and the procedures for support of mobility and session setup in packet domain of UMTS network and in mobile IP are described. Particular attention has been given to the IP multimedia subsystem specified by 3GPP for providing of conversational multimedia services in packet mobile networks. It enables differentiation of the operators on the application and service level while using packet access and SIP protocol for connection establishment and mobility handling. As the new networks have to enable global, always the best access and the continuity of the service to mobile terminal, interworking between packet and circuit networks has also been presented.