Actress Katrina Kaif sang the birthday song for her "Phantom" co-star Saif Ali Khan on the sets of singing reality show "Indian Idol Junior".Shot on Saif39s 45th birthday on August 16, the episode will see the "Kamli" diva singing the song. It wasn39t just Katrina who showcased her singing talent as Saif also went behind the mic and sang songs like "My dil goes mmmm..." and "Shukran Allah". He also strummed the guitar, read a statement. Saif and Katrina -- who were on the sets of "Indian Idol Junior" for the promotion of their forthcoming movie "Phantom" -- were joined by the show39s judges Sonakshi Sinha, Salim Merchant and Vishal Dadlani. Sonakshi39s star mother Poonam Sinha also visited the sets. The episode will go on air on Saturday.