The foxy NEC Flask phone is transparent and lets you see the liquid fuel cell power housed within. What's even cooler is that you can watch the liquid inside drain off in proportion to the power consumed. Since it's still in conceptual stage, we don't know whether the UI is based on touchscreen and/or e-paper technology. However the hip colors offered indicate that it will target the young gals.

NEC has not yet revealed how one can recharge the phone once the power drains.

Source