Noise cancellation
If you are calling from a noisy environment, your phone filters out background noise to make your voice sound clearer to the person at the other end of the line.
Noise cancellation is not available when using the loudspeaker or a headset.
For the best noise cancellation, hold the phone with the earpiece to your ear and the main microphone towards your mouth. Do not cover the secondary microphone on the back of the phone.