In the past, the only way for the hearing impaired to communicate was either in person or by way of the TTY
(teletypewriter); the TTY is a device that's about as large as a laptop computer, and it allows the hard of hearing to type on a QWERTY keyboard and have the communication transferred. However, iZ breaks that barrier; it will allow the deaf to pull an iPhone 4 out of their pocket and effectively communicate. Now, another technical impediment will be on its way out. This is wonderful news.
At first, the technology will only be available through Wi-Fi and the iPhone 4, but it's a safe bet to say that it will eventually filter down to other devices and be able to use cellular service. For now, though, it's quite a start.