This diploma thesis deals with developing multimedia applications on Java Micro Edition platform. The aim of this work is to design and implement the application which could establish a call between two users. The first part of the work describes J2ME platform, its two configurations and profiles. Next part is focused on Session Initiation Protocol and Real-time Transport Protocol. The application design consists of choosing the suitable virtual machine JVM, SIP and RTP libraries. The main part of this work describes application structure, graphic user interface and installation packages creating. It also shows a way of customizing the media stack - Java Media Framework, version Cross Platform