A strong business case has evolved for telephone-based Spoken Language Interfaces. The SLI systems primarily depend on an Automatic Key-Word/Key-Phrase spotting system (ASR) to understand the user's queries and a Text-to-Speech (TTS) synthesis system to respond and to deliver content in an audio form to the user over a telephone. The benefits derived from SLI systems are many, reduced operating costs and improved customer satisfaction being the important ones.

Considering the state-of-the-art in speech technology, the day is not far when spoken language interfaces will be the industry standard for telephone based services, just as we have Graphical User Interfaces for desktop systems. But it is important to bear in mind that the limited capacity of the human auditory memory imposes additional requirements for spoken language interface design. For example, a persistent visual display allows presentation of a large volume of data or information in a tabular form that can easily be browsed. However, audio-only interfaces, such as in voice response systems over a telephone, must summarize information or data into manageable chunks that a user can process and cope with. Another point to note is that, the easier an SLI system is made for the user to use, the more complex does it become to design.