Sure, it has missed the promised August date but it looks like iPhone 3GS is due anytime now. One of our tipster let us know that iPhone 3GS has hit the Apple India website. We are not sure if it has been added today or for the past few days but this definitely is an indication.
[Thanks Raj!]
The iPhone 3GS is been on apple india website from day 1 (9th Jun 2009)