Recording a telephone conversation

I tried to record a telephone conversation. However, when I played it back, I only heard my voice, not the other participant.

I am making sure that I give the standard “I just need to mention that as standard operating procedure this call could be monitored or recorded for training purposes, ok?”

My headphones have one jack that plugs into my laptop. But I am able to make phone calls with it. How do I set it up so that it records both my voice and whoever I’m callings voice?

Personal Recorders do not record both sides of the conversation.

I use a stand-alone recorder and a special microphone I plug into my ear. It works with any telephone or cellphone.