Miley Cyrus celebrated her 16th birthday with tons of colleagues and friends Sunday night at the American Music Awards. You can bet that "happy birthday" was sung in key! Ashley Tisdale, Jordin Sparks, and Taylor Swift sang to Miley backstage! "All the girls, we decided we were going to say 'Happy Birthday' to Miley backstage," Taylor tells US Weekly. "I thought she nailed it tonight," Miley sang "Fly on the Wall" to a screaming audience, including her dad Billy Ray who was in the crowd. Besides her Disneyland party this summer, what did her dad get her for her big day? "A recording studio!" he told US Weekly. That's going to be a hard gift to top next year!