This unit facilitates quick and easy recording of your telephone conversations in the field, such as a pay phone or a cellular phone. All you need is a standard portable cassette recorder and this device and you then have portable recordable telephone recording capabilities. Simply plug the jack into the recorder, place the ear bud in your ear and then place the telephone’s handset over the ear bud. It will clearly record both sides of the telephone conversation, although it may not work on some cellular models. A very handy device to have in the field.