It certainly appears that Apple is working on and prototyping an instant messaging client for future version of iPhone OS. Text strings found in the latest iPhone OS 3.2 beta appear to reference "ChatKit" which was an Objective-C based IM client framework developed by Adium but since left for dead.
The strings found in the SDK reveal that a future IM client developed by Apple might allow users to send pictures (similar to iChat) and would have a similar interface to the included Messages (SMS
