This paper introduces a text entry application for users with physical disabilities who cannot utilize a manual keyboard. The system allows the user to enter text hands-free, with the help of "Non-verbal Vocal Input" (e.g., humming or whistling). To keep the number of input sounds small, an ambiguous keyboard is used. As the user makes a sequence of sounds, each representing a subset of the alphabet, the program searches for matches in a dictionary. As a model for the system, the scanning-based application QANTI was redesigned and adapted to accept the alternative input signals. The usability of the software was investigated in an international longitudinal study done at locations in the Czech Republic, Germany, and the United States. Eight test users were recruited from the target community. The users differed in the level of speech impairment. Three users did not complete the study due to the severity of their impairment. By the end of the experiment, the users were able to enter text at rates between 10 and 15 characters per minute.