There have been several auditory prostheses which have been successful in transmitting some auditory information to what would normally be a deafened auditory area of a deaf patients brain. This effect can be achieved through the use of a cochlear (inner ear) implant (of course, this only for people who are deaf because of problems in their ear, not for those with brain related hearing impairments).
An extensive amount of information on cochlear implants is available here, written by Dr. William House, a long-time cochlear implant researcher. This page outlines the history, workings, and controversy (and there is a lot of it!) associated with these implants.