In 2007, Khalifa signed to Warner Bros. Records and released two mixtapes through Rostrum Records: "Grow Season", hosted by DJ Green Lantern and released on July 4, 2007, and "Prince of the City 2", released on November 20, 2007. His debut Warner Bros. single "Say Yeah" reached number 25 on the "Billboard" Rhythmic Top 40 music chart and number 20 on "Billboard's" Hot Rap Tracks. The song samples "Better Off Alone" by Alice Deejay. Khalifa's vocals from "Say Yeah" appear near the end of Pittsburgh mash up producer Girl Talk's 2008 album, "Feed the Animals", over music from Underworld's "Born Slippy", Usher's "Love in This Club", and the Cure's "In Between Days". Khalifa appeared with The Game, David Banner and Play-n-Skillz at U92's Summer Jam at the USANA Amphitheatre in West Valley City, Utah on August 2, 2008. Khalifa released the mixtapes "Star Power" in September 2008, and "Flight School" in April 2009 on Rostrum Records.