People who want to read to themselves aloud? I don't know that there are enough of these to make a market. But expand this to people who talk on their cellphones and you get a millions. Add in the people who don't want to listen to the conversations. If you can make a device like this, you will get rich.

Actually this probably wouldnt be that hard to do. You may be familiar with noise cancelling headphones, they have a built in microphone on each earpiece, connected to a small amplifier and a speaker. The microphone picks up any external noise and transmits through the speaker an equal but opposite waveform, which cancels out the noise.

Translate this to a cellphone, all you would need extra is another speaker near the mouthpiece somewhere, which could be activated on the phone.

I don't know how well it would work but I'd be willing to bet there would be a significant dB reduction in your voice volume.

copyright :)

Actually, there's technology out there by Knoll (office systems), I believe. It's something called the Babbler, I think. It adds "interference" noises to the environment so that your conversations can't be heard.

It was a good idea, though... just needed more expansion.

Military people in very loud environments (around jets) use a headset with a mouth-cup.

http://www.davidclark.com/HeadsetPgs/h7010.htm