Speech recognizers for the local PC use are designed to work well for most speakers, but accept that some users, because of a strange accent, dialect, or voice, will not get good accuracy. On the local PC this is not that large of a problem because the user can always train the speech recognizer to his/her voice, and if that doesn't work he/she can always use the keyboard or mouse.
If a telephony recognizer does not work well for an individual then he/she cannot easily use the application. Often times it is not possible for him/her to train the speech recognizer to his/her voice. Additionally, many cellular phones (and wired phones) have such lousy audio quality that humans can barely understand speech on them, let alone computers. Failure of speech recognition will also mean failure of the application.
Application designers need to be aware that speech recognition will not work for some users, so the users must have a back-off. A back-off can take several forms:
Often users get poor recognition because they are speaking in a manner that causes speech recognition to make mistakes. Give new users tips on how to use speech recognition, such as provide concise responses.
Detect that the user is having difficulty with speech recognition and provide queries that have fewer or more distinct answers to improve speech recognition accuracy.
Allow the user to respond with DTMF.
Detect that the user is having difficulty and forward the call to a real operator.