Developers have done a little more poking around with iPhone OS 4.0, and it looks like Apple is set to get much more social with the next version of the iPhone. Not only will the new OS include the new gaming network Game Center, but apparently the OS will also integrate Facebook contacts directly into apps on the phone. An options file in the system details Apple trying to include Facebook as one of the choices in the "Add Account" window (where you'd currently hook up your Gmail or Yahoo! account), and apparently Facebook contacts would then be connected into the Contacts list, with things like Events or Photos automatically synced to their own locations on the iPhone.
And lest you worry (like I would) that your Contacts would suddenly be inundated with friends-of-friends or random acquaintances, it looks like Apple is ahead of you -- one of the options hints that Facebook contacts would be marked as a separate "type" of contact on the phone -- "Friends," or something like that, as opposed to business or family contacts.
AppleInsider also has news of a unified contact view as well, so presumably even if the same person is listed in two different types of contacts, you could connect them up. And AI also reiterates what we've heard about iChat being on the phone, so it's possible that you could even Facebook chat from directly within a forthcoming mobile iChat app. Looks like Apple is realizing more and more the power of social connections.