There are at least 2 bands called V.O.S:
1) Voice of Soul (V.O.S) is an R&B group with members 최현준 (Choi Hyun Joon) and 김경록 (Kim Kyung Rok). 박지헌 (Park Ji Heon) was also a member but left in 2010 due to company differences. The group is in 스타제국 (Star Empire) Entertainment.
Their debut was in 14 May 2004, with the 1st album, “The Real”. The hits from the 1st album were 소중한 사람을 위해 (For The Special Person)