1939 Frank Sinatra and Tommy Dorsey USA

In November 1939, in a meeting at the Palmer House in Chicago, Sinatra was asked by bandleader Tommy Dorsey to join his band as a replacement for Jack Leonard (the vocalist, not to be confused the comedian Jack E. Leonard), who had recently left to launch a solo career. This meeting was a turning point in Sinatra's career. By signing with Dorsey's band, one of the hottest at the time, he greatly increased his visibility with the American public. Though Sinatra was still under contract with James, James recognized the opportunity Dorsey offered and graciously released Sinatra from his contract. Sinatra recognized his debt to James throughout his life and upon hearing of James' death in 1983, stated: "he [James] is the one that made it all possible." 

- Wikipedia

I Think of You - Frank Sinatra and Tommy Dorsey (link)