This product works great for being able to use my iPhone ear buds ( 3.5mm) to my home land line phones, which are Panasonic 5.8GHz wireless phones ( 2.5mm). The typical ear buds for most smart phones come with the 3.5mm plug with three rings, which I suspect is for stereo. Price was good at $3.29 with Amazon Prime (no shipping cost).I tried a similar adapter from Radio Shack that did not work. I could hear incoming voice, but the person on the other end could not hear my voice. It only worked one way. It cost $10.00 plus tax, so the Happy Cellular price is definitely a great deal. This product was delivered in less than 48 hours!