How do I record calls on Viber, Skype, Whatsapp, Voxer, Google, Facebook, etc?

There seem to be apps for recording for local or international calls but none for **Internet calls**. Some apps on the Google Play Store claim to be able to record calls on Viber or Skype. I even found some apps not in the play store. I tried some, but I'm not sure if they work. I haven't gotten around to testing any yet. Some reviews of the apps I found seem to be mixed. I don't feel like reinventing the wheel. I have a second phone that I would use except that **sometimes the calls I make require earphones**. If it matters, the phone I use for Viber, Skype, etc calls is a Samsung Galaxy S6 Edge Plus, and my other phone is a Samsung Galaxy Mega. Please don't bring up any stuff about legality.