Chatty is the smartphone that Timmy wishes up for in "App Trap".
She tries taking over his life with many apps and games. She also causes him to miss Trixie's party and texts all of his friends calling them "losers", making Timmy change his mind and try to turn her off.
She then chases after Timmy until he finally gets to a museum where he uses waves to cancel out the phone so he can wish it away.