Hello

This can be done very easily.

The packets sent by the webphone are raw PCM audio packets which can be played as-is by any audio module, so you need only very basic audio handling which can be easily implemented in any languages.

If you are using Java, then it looks like this:

//import required libraries
import java.io.*;
import javax.sound.sampled.*;

//initialize audio
AudioFormat format = new AudioFormat(8000, 16, 1, true, false);  
DataLine.Info info = new DataLine.Info(SourceDataLine.class, format);
SourceDataLine line = (SourceDataLine)AudioSystem.getLine(info);  
line.open(format);
line.start();

//playback (you can pass the UDP packets as-is as received from JVoIP)
//this is usually called many times from your UDP socket thread or on UDP packet received event
line.write(buffer, 0, length);

//close when you are finished with all playback
line.flush();
line.stop();
line.close();

Note: 
You must add proper exception handling for the above code (try/catch). Exceptions might occur if there is no suitable playback audio device.
More details about Java audio can be found here.
If you are interested in both streams (in/out) then you will need 2 separate lines (don’t just feed both streams to the same line).

Alternatives:

1. Third party software:
Use some third-party software which is capable to playback raw PCM packets.

2. RTP stream:
If you have a software which is capable to process RTP packets then just set the sendmedia_type to 1 so the JVoIP will emit RTP packets which can be processed as is by such software.
If you don't need real-time audio, then just use the voicerecording and related parameters to obtain voice files in wave or other formats at the end of each call.

4. Barge-In:
If you just wish to listen into conversation, then you can use the JVoIP itself for the job. It's barge-in feature allows you to bare into any call and create a hidden conference endpoint, so you can hear the conversation. This is often used in callcenters by supervisors. Let me know if you need this.

These kind of things are sent as the usual notifications (as described in the documentation "Notifications" chapter). More exactly you will have the following notifications at the end of calls:

• a STATUS notification with the statustext set to one of the following values: CallDisconnect,Hangup,Finishing,Finished,Call Finished
  (In case if you need to explicitly handle multiple lines, then check the line parameter, otherwise you can process only messages where line is -1)
• a CDR notification is also sent after each call