IP to IP Calls
For IP to IP calls, you will need to check on the box "Direct IP to IP (do not use proxy)" in the Call Control Settings/Proxy Configuration tab. To reach this menu, click on the K icon in the upper left side of the phone, then select Configuration > Call Control Settings and then go to the Proxy Configuration tab. A screenshot of this tab can be seen here.
You will then need to enable this setting by saving it in a configuration file (File > Save As) and then restarting the softphone (Configuration > Restart Softphone).
After restarting the phone, you can place the destination IP address on the edit box of the phone and click on any Line button. The communication will be then established with the other device (another Kapanga Softphone or any other SIP device).