Asterisk Native Sounds are a collection of audio prompts for Asterisk. They will improve quality, reduce CPU usage, reduce latency, and (in some cases) eliminate the need for G729 licenses!
The Asterisk Native Sounds are a collection of alternative sounds prompts for Asterisk. Here's how it works. I had Allison Smith (the voice of Asterisk) re-record all of the sound prompts present in Asterisk 1.2. She provided them to me in the best audio format possible. I then converted them into several native Asterisk sound formats.

cd /var/lib/asterisk/
mv sounds sounds.orig
tar -xvjf /path/to/sounds.tar.bz2

(repeat last step for other formats)
The audio prompts WERE available from the "Extras" category in the Downloads section of http://www.astlinux.org. Now, even better audio files can be downloaded directly from Digium and are included in Asterisk 1.4.

Voice Vector Media (http://www.VoiceVector.com) has released a free full voice-pack containing over 1,500 sound files intended to replace the default sound files distributed with Asterisk. The studio recordings are high-quality and feature a very pleasant and professional female voice speaking American English. These voice-packs are offered in Asterisk Native (sln) format, u-law, a-law, and GSM. Voice Vector Media also offers inexpensive custom recording services to extend and customize this voice-pack. The company's web site lists additional voice-packs in production for a male voice speaking American English and a female voice speaking British English. As of December 19, 2006, the company's website is offering custom recordings at half price.