Professor Oard first described work by IBM India using audio information indexed by numbers which was accessible via a mobile phone. He commented this would not scale and non-literate users do not understand the concept of a hierarchical menu. He then described a method for matching audio called "Query by babbling" (Oard, 2012).
Finding a way to provide information to those with limited literacy is a worthwhile research area. However, there is extensive social science research on verbal communication which the researchers might want to review for insights into how people formate queries. I have come across some of this literature as a student of education, such as Venkataraman and Prabhakar (2014).
Also it happens I spent three weeks in an Indian village and had to communicate with the plumber, the miller and other trades. One insight from this is that they do not use just one language, they use a mix. Also hand gestures play a role.
Smart phones are becoming increasingly affordable and this might provide the opportunity for a visual and audio interface. This interface might also have an educational function, displaying words and teaching written communication, while providing a verbal interface.
Audio interfaces are also useful for those who are literate, but not able to use their hands for typing and do not have sufficient attention to compose a formal audio text query. This applies in formal teams, such as those controlling a metro, military command centers, and flight deck crews. These have been extensive studies of how these people communicate. Part of this is about the formal use of language for directed commands and queries. But part of it is the team members overhearing conversations and acting without being directly asked to do so. Automated systems could be good in this role, where they could eavesdrop on the human conversation, responding and taking action, where appropriate.
Oard, D. W. (2012, November). Query by babbling: a research agenda. In Proceedings of the first workshop on information and knowledge management for developing region (pp. 17-22). ACM.