Recorder

A Warp Whistle is an item from Super Mario Bros. 3. Using it sends Mario (or Luigi) to the Warp Zone. From here, he can skip up from the middle of a world to the start of a later world. Using it in World 1 will allow Mario to warp to World 2, 3, or 4. Using it in a world from 2 through 6 will allow him to warp to World 5, 6, or 7. Using it World 7 or 8 will allow him to warp to World 8. If a second whistle is used while in the warp zone, then the player is taken directly to the World 8 Pipe.

There are only 3 whistles in Super Mario Bros. 3.

World 1-3
Obtained by going behind the black scenery.

World 1-Fortress
Obtained by going through secret door in World 1-Fortress.

World 2-Fire Bros.
Obtained by battling secret Fire Bros. in World 2.

World 5-1 (Japanese version only)
In the Japanese version of Super Mario Bros 3, there's a glitch in 5-1 whitch makes random item appear at the end of the level. It can be done by flying above the stack of blocks at end of the level. After that behind the roulette block the player will noice glitched graphics. By hitting it from far left corner it's transforming into either 5-Up Mushroom or Warp Whistle.

Trivia

 * Mystical Whistle is the name of a Sammer Guy in Super Paper Mario is a pun on Warp Whistle.
 * The song played by the Warp Whistle is from The Legend of Zelda series.
 * A reference to the Warp Whistle is made in the Nintendo Monopoly.
 * Another flute is found in the game Mario is Missing!, stolen from the Teatro Colon by Koopa Troopas. Luigi had to return it to the opera house.