This is a bit of a hobbyhorse of mine. I'd like to see a bluetooth handset that snaps onto your wrist when you're not talking on it.

It could display the time/caller ID/SMSes/notifications like the Pebble, but when a call comes in that you'd like to answer, you'd grasp the "watch face" which would somehow cause the band to unclasp and straighten.

Given that there are bluetooth headsets smaller than a watch, I'm sure it would be possible to build. The trick would be finding an "unclasp and straighten" mechanism that would be reliable, cheap, and unlikely to pinch you when you hang up.