Wonder Girls and Seo Ji Young Irony - Hey Boy 07-03-11 KBS

On September 5, 2007, Good Entertainment, the talent agency for the popular boy band Shinhwa, sent their trainee Yoobin to JYP Enterainment as a replacement for Hyuna. She made her debut three days later in the group's live performance of "Tell Me" on Music Bank .[5]
Their first full-length album, The Wonder Years, was released the following week, on September 13, 2007, with "Tell Me." Due to the last-minute addition of Yubin, the album version does not contain her part; however, the performance version of the song was reworked to include a bridge with Yubin's rap. The single was a hit and reached number one on various Korean television and internet music charts, including KBS's Music Bank.
The choreography for the song was simple and widely imitated: by October, many fan performances of the dance circulated on video sharing sites such as YouTube and Daum[6], including one by a group of policemen who were eventually profiled on SBS's Star King.
Wonder Girls had an extensive promotional schedule for their album and by December 2007, also began performing the second single from the album, "이 바보" (Stupid). They made numerous appearances on variety and game shows, sang live on radio, at music festivals, on music shows and in special joint performances with other groups such as Big Bang. MTV has also aired three seasons of The Wonder Life, a reality TV series starring the girls. In January 2008, however, they ceased promotion of their album to prepare for the concert in United States that were schedule for March 2008. [7]
Wonder Girls are often compare to Girls' Generation. Both groups were debuted similar time and has targeted same market to begin their career. It was very close time that both group gained big popularity and each group's fan consider other as rival. But both groups are known as very good friend to each other.