[Thanks to everyone who sent this in]
Update: AT&T tells us that everything was patched up and good to go as of 7:15 CST.
"Due to an equipment issue, some AT&T mobility customers in Texas may be experiencing authentication issues with their wireless devices. AT&T technicians are working to resolve the issue at this time, and we expect service to be restored later today. We will provide more information as it becomes available. We apologize for the inconvenience."