Cell phones have introduced us to a world where mobility coexists with communication. Combine the mobility of the cell phone with speech recognition technology, and we now have a revolutionary way to access information and conduct business by interacting with computers, anytime, anywhere. What’s more, mobile callers can get to information without extra equipment such as wireless modems, WAP phones, or Palm Pilots; all they need is a simple phone. Speech-enabled services offer the added benefit of gathering and presenting information all in the auditory modality. So when driving or on the go, callers can attend to their environment without having to look at a screen or press buttons. Voice user interfaces (VUIs) are not without their challenges, though. Audio is transient and cognitively demanding. In addition, callers have high expectations of the technology’s capabilities and assume that any utterance of theirs should be recognized by the system.