HD Voice is a relatively new technology that hasn't really taken off too quickly around the world yet, but it got a huge boost today with Telstra announcing it's switched its entire NextG network over to support HD Voice.
HD Voice offers a much higher quality of voice calls on compatible hardware. It samples a larger frequency and suppresses background noise to provide a much clearer call quality.
The only catch with the new technology is that you need handsets that support it on both ends of a phone call for it to work. At the moment, there are only five compatible handsets, and four of them are Nokias: The Nokia 6720, E52, E72 and N8 and the HTC Desire S. The Xperia Neo will also support HD voice when it launches next month.
That said, the technology is still kind of new, and we can expect to see more compatible handsets launch over the coming months, especially now that Telstra has launched the technology.