Today AT&T has released and iPhone app (iTunes link) that lets customers tell them where they drop calls and experience other general network failings. The app, dubbed 'Mark the Spot', allows you to choose what kind of failures the iPhone is having and lets you plot against frequency of the outage.
Good for them for at least listening at this point, though we're not sure how you submit your issue if you have 'no service' or 'data failure'. We're also hoping they have some pretty serious data centers lined up to take the submissions.