The band Metric, who wrote & performed Eclipse (I'm All Yours) on the official Eclipse soundtrack is appreciative for their opportunity to be a part of the Eclipse soundtrack. According to their most recent interview with Scene Louisiana this was a great honor because Howard Shore (the composer of the score) worked with them on it & even put the melody to the song throughout the score.
Here's what Emily Haine's had to say:
"We wrote the theme song for the Twilight movie with Howard Shore, the composer . . . The end of the movie is our song, written with him. He came to us saying, ‘Will you write a song with me?’ We needed to write the theme that culminates at the end of the movie, and then throughout the whole movie, you can hear that he took our melody that we wrote, and he has the strings playing it like seven times.It was really nice to learn from him how the process works in composing. A very preliminary sort of glimpse, but that’s been exciting for me . . . It’s always flattering when people ask you to do songs in a soundtrack, but it’s wholly another level when they ask you to write the score. That’s definitely something we’re interested in doing more of."
via Twilight Examiner.