The official home page of Ekiga is http://www.ekiga.org/. This site offers answers to frequently asked questions as well as more detailed documentation.
For information about the support of the H323
teleconferencing protocol in Linux, see
http://www.voip-info.org/wiki/view/H.323. 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
http://www.asterisk.org/. Find information about at
http://www.voip-info.org/wiki-Asterisk.