I see the occasional fake AT&T message all the time, but got 15 variations on this theme today.  Looks like a baby spammer playing with a new toy.  Senders included:
Kristi Leal (support@irs.gov)
Sally Moser, Jody Grace, Loretta Bragg (all at alerts@irs.gov)
Emily Delgado, Johnnie Espinoza, Luz Wyatt, Bernadette Shelton, Ruth Hodge, Brice Herring, Mabel Luna, Amelia Weeks, Chelsea Mcdowell (all at robot@craigslist.org)

Subjects included:
Your AT&T bill is ready to be viewed
Your outstanding AT&T online bill
Your AT&T bill is ready for download
Your AT&T bill is ready to be paid now.
Pay your AT&T bill online

The text of the early ones were full of errors:

your online bill is ready to be {l2}
dear {l3} customer,

a new bill for your at&t {l4} is {l5}.

any {l6} {l7} after your bill period {l8} will not be {l9} in the bill amount listed directly below. if you have made a recent payment, please refer to the current balance on the account overview and the bill & payments pages.
service account ending in bill amount due date
{la} {lb} ${lc}{ld}{ld}.{ld}{ld} 08/06/2012

But eventually they figured out how to use their spamming software:

Your online bill is ready to be viewed

Dear Valued Customer,

A new bill for your AT&T account is ready.

Any operations completed after your bill period expires will not be reflected in the bill amount listed directly below. If you have made a recent payment, please refer to the current balance on the Account Overview and the Bill & Payments pages.
Service Account ending in Bill Amount Due Date
Internet access 7 $866.53 08/06/2012 (amounts ranged from $100 to over $900)

Log in to online account management to view your bill and bill notices, maintain your email account or make a payment. If you are not registered for online account management, you must do so to view and print your full bill and bill notices at www.att.com/managemyaccount.
Log in to online account management to view your bill, maintain your email account or make a payment.

Thank you for choosing AT&T. We value your business and look forward to serving you!

Thank you,
AT&T Online Services
www.att.com

The Login buttons and other hyperlinks lead to sites that I assume intend to do me harm.