This unit is the simplest and cheapest way to record telephone conversations but it is also the most versatile and portable and can be used on almost any phone (especially public phones, but even wireless, cellular, and cordless phones).  One end of a 4 foot cable has a pickup device with a suction cup mount, and the other end has a 1/8th inch mini jack.  Just by sticking the suction cup end on a phone, and plugging the other 1/8th inch jack into a microcassette recorder or any standard tape recorder or recording device with a 1/8th inch (small headphone size) mic jack, you now have an instant portable telephone recorder. Caution: check the laws in your state regarding two-way telephone recording.