This comfortable, Motorola hands-free headset provides great sound quality on both ends of the conversation. The earpiece lays on the ear, outside of the ear canal, eliminating the discomfort associated with in-ear headsets. 2.5mm stereo phone plug. The 2.5mm plug is standard on most cordless home phones. However, most current cell phones / smart phones require a 3.5mm plug. A 3.5mm male jack to 2.5mm female plug adapter is included with this item.