Silent speech recognition
NASA has been working on a system to recognize sub-vocal speech. With this system, a person need only mouth the words without actually uttering anything. For very small vocabulary tasks, they were able to achieve 92% accuracy. Someday, all of our cellphones will have this as a builtin, allowing you to converse while in the movie theater without bothering anyone around you (except maybe your date). In the mean time, its probably just best if you turn the phone off.