Natural speech is the modality used most often when communicating with other people. This makes it easier for a user to learn the operation of voice-activated services. As an output modality, speech has several advantages. First, auditory input does not interfere with visual tasks, such as driving a car. Second, it allows for the easy incorporation of sound-based media, such as radio broadcasts, music, and voice-mail messages. Third, advances in text-to-speech (TTS) technology mean that text information can be transmitted easily to the user. Natural speech also has advantages as an input modality, allowing for hands-free and eyes-free use. With proper design, voice commands can be created that are easy for a user to remember. These commands do not have to compete for screen space. In addition, unlike keyboard-based macros (e.g., ctrl-F7), voice commands can be inherently mnemonic ("call United Airlines"), obviating the necessity for hint cards. Speech can be used to create an interface that is easy to use and requires a minimum of user attention.