AT&T app is built-in as firmware update. You must have missed the update where they updated the logos and making the signal bars appear to be twice as much as actual signal.
I'm shocked personally that AT&T nor Apple have iPhone-optimized websites.... irony? I think so.
Here is a handy AT&T app that shows your minutes left etc..
http://itunes.apple.com/WebObjects/MZStore.woa/wa/viewSoftware?id=312324583&mt=8
A someone who has AT&T for cell, dsl, and local phone service, I would love an application.
Why did they not make it part of the deal that apple has to make them an application for the phone.
People are right, this is a glaring omission from the App Store.
Heck it should have been available on the phone before the app store.