Get started with VoIP [closed]

Answer 1

Edit: I would recommend this solution with Apache web server http://www.openvbx.org/ .

For native sip project you may wanna check http://code.google.com/p/csipsimple/ as well as this may be good starting point.

For further reading I would suggest this article, which may be useful for how to start with VoIP on bigger scale and the costs of it.

For simple solution