AT&T has the lowest customer service rating of American mobile phone companies. Of course that's like asking what's worse - Ebola or Rabies?
This is not because of their retail staff. They must give them powerful drugs, because, despite working for a moderately evil corporation, they're remarkably cheerful.
Their web site though, that's part of what makes them "Rabies" rather than just "Ebola".
For example, for the past few days I've been trying to follow up on some extensive bill slashing changes. In particular I've been trying to find a current contract summary for our family plan. I think I've found the best that ATT offers, but they have one of the worst web sites I've ever come across. 
As of Nov 2011 try this. Don't click on the tabs, but mouse over to see the substructures. Note you may have to authenticate repeatedly.
- Go to your AT&T mobile account page. Look at the top menu structure. It will say myAT&T, with "tabs" like "Overview", "Bill & Payments" and so on. Depending on the services you use some are not useful, but they will still appear. The tabs that are useful for a mobile-only customer are
- Bill & Payments: see current bill statement
- Wireless: usage and recent activity
- Profile: user information
- From user information look for "Contract Information". Click Customer Service Summary and Contract. Now you get a popup window. In there you find several options including two that, despite their names, both show a similar PDF (these links may actually work as shortcuts once you're authenticated):
- Wireless customer agreement: This is the real deal. CSS plus six pages that summarize your true contract 
- Customer service summary (wireless): Just the CSS
- Alternatively, AT&T's "Your Phone CSS" email provides this link with goes to a screen I can't find when I navigate the site, in fact it seems to be a outside of the tabs they define and possibly a separate web site: https://www.wireless.att.com/olam/loginAction.olamexecute?target=CSS. There's a trick here. Unless you read carefully, you'll hit the "continue" button -- that will just take you back to the main site. Instead, look for the link under the wireless number drop down and click that. You get the PDF contract summary.
Note that under the Wireless tab is a "Rate Plan" link, but it only shows voice plan.
So, in summary, to determine your actually currently contracted services for a family plan you need to print/view a PDF for each individual family member and do the sums to produce an integrated view.
I wonder if there's a medical term for the psychosis induced by dealing with AT&T?
Next up: How to track SMS use.
 The primary flaw is that AT&T mixes marketing with service. There are other reasons, but that's the primary dysfunction. What I want to know is mixed with what they want to sell me. A secondary reason, is that they choose not to invest in areas that allow customers to see what their contracts are. Those investments have a low return on investment and will not contribute to someone making VP. It's just a happy accident that it works this way.
 Update: AT different times I got different PDFs for different users. Only my wife, a secondary number, produced the full six page report when I requested a "wireless customer agreement".
Update 12/11/11: I've studied the PDFs in more detail. They are quite hard to interpret, particularly for a family plan, but, with some study, they do show the current contract. I think the "wireless customer agreement" is a copy of the original contract, but the "customer service summary" is the current contract.