Ambient Corporation has developed the Audeo, a neckband that picks up inaudible signals from a person's voicebox and can translate those signals into speech! The signals are sent to a computer for translation. In order to use such a device, the user must be trained to deliberately encode the words they wish to communicate to the neckband area. The version demonstrated in this video can translate about 150 words, but a new version will use individual phonemes instead of words, so although the "speaker" will have to be slower and more deliberate, the computer will be able to translate an unlimited number of words.
You may wonder what the purpose of such a device would be. The most obvious use is for people who have lost their ability to speak due to diseases like ALS. Ambient Corporation has used the same technology to allow people to control wheelchairs using their thoughts. I bet the military and the CIA would love to have a way to communicate silently. If this becomes available to everyday consumers, every kid at school will be clamoring for one, especially for use during tests!