Conversation so far:
Who has he collaborated with?
label-mates The Grace.
Has he had any other collaborations?
Yoochun.
Did he work a lot with Yoochun?
Kim and bandmate Yoochun released a self-composed single "Colors (Melody and Harmony)/Shelter.
What soundtracks did he work on?
Kim sang "Love" for the soundtrack of the film Heaven's Postman in.
Was this a hit?
CANNOTANSWER.

Question: What other soundtracks did he do?
Self-contained rewrite: Besides the Heaven's Postman soundtrack, what other soundtracks did Kim Jae-joong work on?