From W3C's VoiceXML 2.0 specification (http://www.w3.org/TR/voicexml20):
	 :	VoiceXML is designed for creating audio dialogs that feature synthesized speech, digitized audio, recognition of spoken and DTMF key input, recording of spoken input, telephony, and mixed-initiative conversations. Its major goal is to bring the advantages of web-based development and content delivery to interactive voice response applications.

For more information go to http://www.voicexml.org/