title: SIP communication open source
body: <p>I was trying to implement the SIP concept in my app. For that I found <a href="http://www.portsip.com/voipsdk.html" rel="nofollow">PORTSIP</a> sample code. It is working fine with the given credentials (domain, username, password). But it is a trial version, not an open source. </p>
  
  <p>Does there any open source for the VoIP calling. Please help me out that what steps should I follow to implement the audio calling via SIP.</p>