I could be wrong but I do believe that is a mic for the noise cancellation program that the device has. It picks up the ambiant noise around you and cancells it out.
I believe the video camera uses the phone mic for its recording
No good answer about this? I doubt it is a mic for speaker phone calls... I believe one pinhole on the back is a speaker phone mic and the other is noise cancellation. The thing by the camera looks like a speaker. I guess it could be a mic for video... easy way to test would be to run your finger near it and then elsewhere on the back to see if the video sound gets louder when you get closer to it.