He later moved into dormitories with fellow trainees and was trained in areas of singing, acting, and dancing. He was featured in a music video of The Grace's Dana whilst he was being trained as a solo singer in 2003. A year after, Choi made a brief appearance in short drama, Precious Family and again in 2005 in the KBS drama Eighteen, Twenty-Nine as young Kang Bong-man, while in 2006 he played the supporting role of Park Sang-woo in drama Spring Waltz.