In order to un-register Real Softphone from our network (and PUSH server), select Incoming calls to Off.
** Before uninstalling Real Softphone from a mobile device, ensure you un-register first.
Click Settings -> Incoming Calls -> Off
Now Real Softphone will no longer ring on incoming calls, but you can still use the app to call out.
To re-register and enable to receive incoming call again, simply repeat the above and select Push notification.