If this weren't so expensive: "Babble is the only voice privacy device currently on the market that offers voice confidentiality during a phone conversation. It camouflages conversations about rash decisions, or discussions about rashes. Babble accomplishes this by using a pre-recorded script of the user’s voice, which is “babbled” and emitted from proprietary speakers positioned outward from the user. The “babbled” voice provides cover, making a phone conversation unintelligible to individuals surrounding the user. “White noise” simply masks overall interior sound, Babble “babbles” the users voice keeping private phone conversations private."
http://www.thebecollection.com/catalog/product/5-babble-voic...