Some days or months before the iPhone 4 announcement that transpired today, it's clear that Apple and AT&T very likely had a number of planning sessions. The result was an agreement by AT&T to offer a number of iPhone customers currently under contract an option to upgrade to iPhone 4 this month. The unsurprising result was undoubtedly a peak in traffic to the AT&T iPhone account management server page. The surprising result was that, despite the advance planning, the AT&T site may have been unprepared for the traffic.
According to a Computerworld post by Gregg Keizer, the result was that the site could was either taken offline intentionally or, probably more likely, could not handle the volume.