Smule has released Leaf Trombone World Stage, its latest social instrument application for the iPhone and iPod touch. First previewed during the iPhone OS 3.0 event in March, Leaf Trombone is Smule’s first “massively multi-player” musical game, expanding on the iPhone-as-instrument concept seen in the company’s prior release Ocarina. Trombone features a self tutorial mode, judging capabilities which players can use to provide…