Cochlear implants are widely available, though expensive--about 190,000 have been installed in the ears of people suffering from profound deafness. They have some serious limitations, some of which will take lots of time and effort to improve: the hearing restoration is very limited, for example (click here to hear what speech sounds like to someone with a cochlear implant). But the Cochlear Implant Lab at the University of Texas at Dallas is awaiting FDA approval for an idea that could dramatically improve the usability of cochlear implants right away: link them with smartphones.
The two main reasons to link a cochlear implant with a smartphone are simple: control and record. Current cochlear implants have very little in the way of flexibility, with the user mostly unable to adjust the implant to suit the sounds in the user's environment, but a smartphone app could fairly easily be written that would enable all sorts of controls, including volume and frequency modulations.
Also, doctors and researchers find it very difficult to get much data from cochlear implant patients--the space requirements are, as you'd imagine, very tight, so there's no room for a universal recording device. Smartphones could very easily record and store all sorts of data so doctors and researchers could better understand the way cochlear implants work, and the ways they could be improved.
Current status: Enmeshed in the FDA approval process.
Runners-up: There are four major manufacturers of regular (i.e. non-smartphone-compatible) cochlear implants: Cochlear, Advanced Bionics, MED-EL, and Neurelec.