Simple Voip server for Ubuntu

You can use asterisk with only SIP or IAX2 protocolos.

apt-get install asterisk vim /etc/asterisk/sip.conf <--- add users here vim /etc/asterisk/extensions.conf <--add dialplan here

so basic setup: add user to sip.conf with field

[user1]
.....
context = mydialpan
.....
[user2]
.....
context = mydialplan
.....

Then edit extensions.conf like:

[mydialplan]
exten => 1001,Dial(SIP/user1)
exten => 1002,Dial(SIP/user2)

then connect with some softphone like xlite/ekiga to asterisk and dial 1001 or 1002 to connect with correct user.

here is some useful link http://hubpages.com/hub/How-to-Install-Asterisk-on-Ubuntu-Setting-up-Asterisk-PBX

With the latest Ubuntu desktop and Empathy, you should be able to do chat/voice/video in the local network without any server, by creating a "People nearby" account.

Alternatively, I suggest creating a Jabber/XMPP server, and look for a cross-platform (or not, depending on your needs) client that has Voice support.

Here is the official documentation of Ubuntu Server to install jabberd2.

https://help.ubuntu.com/10.04/serverguide/C/jabberd2-server.html