The official home page of Ekiga is http://www.ekiga.org/. This site offers frequently asked questions as well as a more detailed documentation.
For information about the support of the H323 teleconferencing protocol in Linux, see http://www.openh323.org/.This is also a good starting point when searching for projects supporting VoIP.
To set up a private telephone network, you might be interested in the PBX software Asterisk. For more information about this project, see http://www.voip-info.org/wiki-Asterisk.