Horse Call

The Horse Call is a horseshoe-shaped flute acquired by Link in Twilight Princess.

Location
The flute was made by Ilia as a gift to Link for his journey from Ordon Village to Hyrule Castle. Before Link is able to depart, however, a group of Bulblin raiders appears and captures Ilia and several of the other Ordon children. Eventually, Ilia is found under the care of Telma in Castle Town, though suffering from memory loss. In a quest to restore her memory, Link recovers the flute from Impaz in the Hidden Village, where Ilia had been held captive. After presenting the flute to Ilia, she regains her lost memories and is finally able to give Link his gift.

Uses
The Horse Call is used to play Epona's Song to summon Epona anywhere in Hyrule Field, similar to the Epona's Song from Ocarina of Time. It eliminates the need for Link to locate patches of Horseshoe Grass.

Trivia

 * By the time Link acquires the Horse Call, he can already warp almost everywhere in Hyrule, thus making the Call almost useless at that point in the game. However, riding Epona is faster than both walking and dashing in wolf form, so it may be helpful in side quests (such as collecting Poes, Heart Pieces, etc.) but it is virtually useless in the main quest.

Super Smash Bros. Brawl
The Horse Call appears as a sticker in Super Smash Bros. Brawl.