This softphone application for Mac OS X functions as an IAX client for the Asterisk PBX.
With LoudHush you can initiate, answer, hold and transfer voice calls using your computer. LoudHush is written in Cocoa/Objective-C and integrates within the OS X environment.
This program requires Mac OS X 10.3 or later, an Asterisk account, speakers and a microphone. In the unregistered version, the program quits five minutes after being launched.