Mobile (cell) phones are getting smaller and smaller. Many include a radio, MP3 player or perhaps both.
The problem with audio features such as this is that often a relativly bulky sterio headset is required. If the headset is small, often the connecting wires are the part that take up all that room
in your pocket.
Bluetooth headsets go someway to solve this problem, but that's one more peice of equipment to carry/charge/etc.
This idea is to simply have a Bluetooth headset or earbuds that dock into the phone's body when not in use. Earbuds can be made to be very small and have some sort of power retention device that recharges from the phone's main bettery when docked.
Of course, when docked, such earbuds would be utilised as the phone's main earpeice.
Ideally, a user could utilise both 'buds for sterio listening, or just one to make/recieve calls if that was required. Thus one would have a tiny microphone built in - and despite what people think, such a microphone does not have to be close to the users mouth.