At CEATEC Japan 2011 exhibition , KDDI company showed a smart phone that does not have usual speaker. Sam developer calls the device smart phone with new sensations of hearing .
It uses piezoelectric speaker element thickness not exceeding 0.6 mm.
When the user is talking on the phone, the piezoelectric element vibrates.
KDDI note that the sound is even cleaner than a conventional speaker. Interestingly, it is not necessarily to completely cover the ear.
In addition, piezo speaker is smaller, cheaper, and it consumes less electricity.