A simple way to connect an audio recorder to a normal home phone line.  One end of this cable plugs into a 3.5mm microphone jack on a recorder (any kind of tape or digital recorder that has such a microphone jack will work), while the other end plugs into a standard telephone jack in your wall.  The cable contains the necessary filters to convert the signal in your telephone line into a simple audio feed for your recorder.  This will not connect to a computer microphone jack, only to an audio recorder.
Please note that this cable only connects to a standard telephone line.  It does NOT connect to any kind of VOIP (internet based) phone system, nor any kind of multi-line phone set up, and obviously not to a cell phone.  The reason this cable is very popular, is because it will connect to any phone jack in the home, and still record every phone, including all cordless phones.

Specifications:

• Mic jack
  • 3.5mm Mono
• Phone jack
  • Standard RJ11 single line
• Cable length
  • 150cm (approx. 5 feet)
• Colour
  • Only available in black