AT&T just released a free app called AT&T myWireless Mobile that allows you to view information about your AT&T account and manage your account from your iPhone. It is a very useful app, and frankly I'm surprised that it has taken AT&T this long to release something like this.
Before you can use the app, you must first establish a myWireless account on the AT&T website if you don't already have one. The same password that you setup on the website provides account access on your iPhone. From the main screen of the app, you can choose to see information on your phone bill, see information about your monthly usage, and manage features on the iPhone. When you are using the app, those three options appear at the bottom of each screen.
From the Bill Summary screen, you can find out how much you last paid, how much is due, and even view a PDF of your full bill. There is also a button (not shown on the below screen picture) that allows you to pay your bill by credit card or by a withdrawal from your checking or savings account:
On the Usage screen, you can view the number of minutes used in your current cycle, either for any individual phone on your plan for for the "Group" (all phones on your plan). You can also view individual data usage (text messages and MB of Internet use) for each phone. Looking at this screen, I am reminded that one of these days I need to tell AT&T that I spell my first name "Jeffrey":
Finally, on the Features screen, you can see all of the different plans that are available for the iPhone and checkmarks to indicate which plan you have. You can tap to get more information on each plan, including the cost and the terms and conditions, and the app even gives you the ability to add plan features from the iPhone itself. You can see below that I've pasted three screens together so that you can see the many different features listed as you scroll through this screen:
This is very handy app. It takes a little longer than it seems it should for each screen to download data, but even with that slight delay it is much faster to manage an account using this app on an iPhone than it is to access the AT&T website on a computer (or for that matter using Safari on your iPhone). And the app is free, so you really have no reason not to get it.