GunningForSafety has found some clues that apple is planning to integrate Facebook into iPhone OS 4.0 just as webOS and HTC have done in the past. Currently iPhone has support for user accounts of Gmail, MobileMe, Yahoo etc and looks like Facebook account would be included in the new OS too.
It looks odd that Facebook would be added in this list because Facebook is really different from all these services since it’s a social network and they are email accounts. But iPhone could use it for your Facebook contacts, profile pictures, events, messaging framework and so much more.
With this it seems clear that Apple would implement Facebook Events into iPhone’s Calendar app and may also add Facebook friends list as iPhone contacts. With all this, Apple may create a new contact type for Facebook contacts and they me be listed as friends in your iPhone instead of showing them as just normal contacts.
People have lot of expectations from iPhone OS 4.0 and they are waiting for it to release with new iPhone 4G. Features like Facebook integration would surely please both Apple and Facebook fans.