AT&T sent out a survey to iPhone owners asking them to rate it's capabilities and included on the survey was iChat. Hopefully it's in the works!
http://www.engadget.com/2007/07/08/atandt-survey-hints-at-ichat-application-for-iphone/
http://www.engadget.com/2007/07/08/atandt-survey-hints-at-ichat-application-for-iphone/