RazorianFly points to a Tweet from developer John Heaton revealing strings within the iOS code making reference to iChat-related services such as Jabber and AIM that are not currently supported directly by Apple on iOS.
Speculation has naturally turned to the possibility that Apple is working on an application to integrate full iChat capabilities into iOS, although that may be something of a stretch. Rather, it seems more likely that the code is part of a general IMService framework to support all of Apple's messaging protocols regardless of whether support for the actual services is included on a given platform.
Apple currently supports a variety of messaging and video communication services on its Mac OS X and iOS platforms, using a somewhat complex array of applications. On iOS, Apple's new iMessage service is handled through the Messages app that also handles SMS and MMS on the iPhone, while FaceTime is handled through the Phone app itself on the iPhone and a standalone app on the iPod touch and iPad 2.
On Mac OS X, iChat handles basic messaging services such as AIM and Jabber, as well as audio and video chat capabilities of those services, while FaceTime is supported in the form of a separate application. iMessage is not yet supported on Mac OS X, although code strings and rumors have suggested that the feature will be coming to the Mac.