According to the keen-eyed folks at Pocket-lint, Apple has posted an iPhone 4 screenshot on its American website that shows the option to open an attachment in “Keynote”. Pocket-lint points out that Keynote, which is part of the iWork app suite, is only available on the iPad and not on the iPhone.
This must surely be confirmation that iWork, comprising the individual apps Pages, Numbers and Keynote, will be available for iPhone 4? Obviously the facility to use Keynote when opening an attachment in email must exist in iOS 4, otherwise they wouldn’t have a screenshot of it. Even so, it seems a little strange for Apple not to trumpet the inclusion of iWork – it’s certainly not been shy about mentioning that iBooks is on its way to iPhone 4 and iOS 4. Apple has since taken down the image, and replaced it with one that shows the option to "Open in 'iBooks'” instead, but you can still see the iWork screenshot on Pocket-lint if you follow the link.
Source: Is Apple’s iWork Coming to iPhone 4? | Talk iPhone - iPhone News Blog and Forums