A free program for Android, by GlintBlue.

If you want to make a good-sounding recording of your phone calls or voice messages, you need to do a lot of settings and adjustments. You need to use a good quality microphone, make sure it is not too close to the phone’s speaker, and use a good quality phone line. 

Reco Call Recorder – Voice Rec is a free call recorder and voice recorder app. It allows you to record all your phone calls, voice messages, and conversations with your friends and family. It is a very simple app with a user-friendly interface. All you have to do is install the app and start recording.

The user interface is very simple.