What is VoiceXML?
VoiceXML is a language for creating voice-user interfaces, particularly for the telephone. It uses speech recognition and touchtone (DTMF keypad) for input, and pre-recorded audio and text-to-speech synthesis (TTS) for output.
http://www.voicexml.org/voicexml/Review/features/Jan2001_what_is_voicexml.html