Most devices designed to help the hard-of-hearing simply amplify sound. This approach doesn't work well for people with severe defects in the outer or middle ear. Daewoo Technologies of Lyndhurst, N.J. has developed a telephone that takes a different approach: sending vibrations directly to the inner ear through the bones in the head. We hear mostly by "air conduction," with sounds traveling through the ear canal and middle ear to the inner ear, where they are translated into nerve impulses that go to the brain. But we also hear via "bone conduction," and Daewoo's phone exploits this effect. A knob in the center of the earpiece is pressed to a bony part of the head and transmits vibrations directly to the inner ear. The phone's makers say the instrument could also be useful for people with normal hearing who work in noisy environments such as construction sites.