KCall is the telephony application of Kontact. It supports computer telephony integration and at the same time integration into KDE's infrastructure. KCall does this by using KDE's addressbook, which in turn can be a server-based groupware addressbook. KCall uses the Decibel realtime communication framework for call management.
VoiceBuntu (formerly Ubunterisk) is an Ubuntu-based live CD that uses Asterisk and VoiceOne to provide VoIP service without any system installation process. VoiceOne is a Web-based GUI for the Asterisk PBX. Ubunterisk can be used as a phone client as well as a PBX server. Ubunterisk can be administered either remotely or by accessing its local GUI. A capser-rw filesystem is used to store the system's data persistently.
Sofia-SIP is a SIP user agent library, compliant with the IETF RFC3261 specification. It can be used as a building block for SIP client software for uses such as VoIP, IM, and many other real-time and person-to-person communication services. The primary target platform is GNU/Linux. Sofia-SIP is based on a SIP stack developed at the Nokia Research Center.
OrderlyCalls is a Java integration component for the popular Asterisk PBX. OrderlyCalls contains support for the Manager protocol as well as FastAGI. OrderlyCalls uses a Named Service approach to providing telephony services to your Java applications, and is configured with a user-extensible XML file. OrderlyCalls also offers native support for running inside J2EE Servlet Containers such as Tomcat, so you can easily add telephony functions to your Web applications.