Apple and AT&T have worked closely together on iPhone throughout its development and looming rollout. That much is certain. But the two companies may be working on some rather interesting service integration with iTunes and a special dashboard widget for OSX users. According to a source I spoke with from AT&T, the two companies are working to enable iPhone users to view and administer their AT&T account from within iTunes itself.
In this arragement iTunes would allow you to view your bill, minutes used, add-on features like ringtone downloads, etc., all right within iTunes. The company may also offer a simple dashboard widget which displays minutes used as monthly bill status. Interesting.