A key feature of iPhone OS 4.0, according to a Business Insider source at least, will be in-built Facebook integration. "But I've already got Facebook on my iPhone," we hear you cry. However, that's just a stand alone app, integration would mean a lot more Facebook features for your iPhone.

For example, the function that is already available to sync your Facebook friends with your iPhone contacts could be expanded and enhanced so that all of your iPhone contacts contain more of their Facebook info, such as birthdays and email addresses. 

It may also mean that you could send Facebook messages, or post on your friend's walls, directly from your contacts, as easily as you now send a text.

Business Insider also says that Apple may incorporate Facebook Connect directly into its SDK so developers can easily add Facebook features to their apps.

The changes could be revealed by Steve Jobs, or another Apple top-bod, at Apple's Worldwide Developers Conference keynote on June 7. If they are, expect the over-keen audience members to whoop and cheer. If the next-gen iPhone is announced during the keynote, as is rumoured to happen, expect an outpouring of emotion from the audience the likes of which are normally reserved for telly evangelists.