Chatter inflicts damage and may confuse the target. This move allows the player to record his or her voice using the Nintendo DS's microphone to play back during the attack.
The chance of confusing the foe is determined by the volume of this recording. The higher the volume of the recording is, the higher the chance of confusion.
Bold indicates a Pokémon which gets STAB from this move. Italic indicates a Pokémon whose evolution or alternate form gets STAB from this move.
Trivia
Chatter is the one of only two moves that cannot be Sketched, presumably due to audio limitations. This makes it the only true signature move. The other is Struggle.
When a person's voice is recorded for the attack, the noise will always be distorted, possibly a failsafe to prevent foul words from being emitted by the game.
After using Chatter outside of battle, the Pokémon's cry will be temporarily changed. In the profile, the cry will be what was recorded. Moves such as Growl, Howl, and Outrage will change as well due to its cry being changed. This will be reset when the Pokémon is deposited into the PC.