i noticed the following comment (by Sriram) in the blog review (http://thenewsdose.com/2008/11/22/ghajini-music-review/):
"Sonu had actually sung the song originally - but prasoon it seems made alterations to the lyrics later and Sonu wasn't available later to record it again - and so Jaaved ali came on board!" is that true guys? any idea?? because otherwise i also wonder why ARR did not give Sonu the full song, if he could do such a splendid job for humming why don't just make him sing the whole song? i don't see anything special in Javed's voice to bring him in, infact honestly speaking there is something odd in his voice, don't know what, just did not like it much. and if he had chosen Javed to sing it then why got Sonu for humming, could not Javed do the humming?? just curious. - Jahanzeb
