A Bluetooth speaker is implanted into the thumb, and the corresponding microphone is in the little finger. The surgical procedure will involve removing the last few centimeters of bone from the finger and thumb, and replacing them with hollow titanium which will contain the actual electronics.-- Alx_xlA, Feb 06 2009 (Old joke) Japanese man on train has the technology you describe. Explains it to intrigued westerner. 10 mins later, starts talking without raising hand. Explains 'That 10 minute ago Japan technology. New technology - silicon chip in lip, silicon chip in ear.'-- spidermother, Feb 07 2009 Not recommended for divers. Signalling "OK" will just put you into a feedback loop that will ultrasonically kill anything in a 5 metre radius-- MaxwellBuchanan, Feb 07 2009 random, halfbakery