SIP Communicator is an audio/video Internet phone and instant messenger written in Java. It supports some of the most popular instant messaging and telephony protocols such as SIP, XMPP/Jabber (and hence GoogleTalk), AIM, ICQ, MSN, Yahoo! Messenger, IRC, Bonjour and still counting. The development of SIP Communicator started out at the University of Strasbourg, France (http://www.unistra.fr) but has grown to include members and contributors from (alphabetically) Brazil, Bulgaria, Cameroon, China, France, Estonia, India, Germany, Japan, Romania, Slovakia, Spain, UK, USA, and others. Some of these contributors have joined the project after successfully participating in the 2007 and 2008 editions of Google Summer of Code. SIP Communicator is based on the OSGi (http://osgi.org) architecture using the Felix implementation from Apache (http://felix.apache.org). This makes it very extensible, particularly developer friendly, and very useful to learn while in the university. Needless to say SIP Communicator is completely Open Source / Free Software, and is freely available under the terms of the GNU Lesser General Public License.