You can record any parts of your active calls simply by tapping the record icon. It will start recording, next tap and the recording stops, if you want to start recording conversation again during the call tap the record icon again. When you want to listen to the recorded messages go to Recent calls menu where you can see all calls with associated recordings marked with the “speaker” icon. Click on it to see the audio player’s controls which allow you to hear the message, switch to loudspeaker and use a seek/progress bar.