They are called Vuvuzelas. I refer to them as atmosphere killers. If you plan on watching the World Cup in South Africa you better get used to hearing the annoying horns blaring constantly. Fans have complained and coaches and players hate them. They make it near impossible to communicate between players and coaches on the field. It's one thing if its yelling and screaming from the stands that prevents players from communicating it's a another thing when it's the following.
The horns rob the game of creative songs and chants that make soccer unique from other sports in the United States. And for most Americans that watch the game every four years you wont get a chance to appreciate chants between The United States and England supporters. Fans watching on Television will have to choose between the prospect of muting the sound or missing out on Martin Tyler calling the match, which is very different from Joe Buck calling a game.