"U-verse service has been restored for the vast majority of our customers affected by the outage," an AT&T spokeswoman said in a statement Thursday. "We expect any remaining customer issues will be resolved this morning. We will provide a credit to customers who were affected. We know our customers count on their U-verse service and we apologize for the inconvenience."

To the frustration of affected customers, AT&T had previously revealed little about the precise cause of the outage and how many of its customers were out of service as a result. Based on customer accounts on outlets such as DSL Reports, most of the problems leaned southward and eastward, hitting parts of Texas, Louisiana, Kentucky, Georgia, Tennessee, Florida and Arkansas. However, customers as far north as Detroit also reported U-verse service issues this week. (See AT&T Faces Backlash Over U-verse Outage and The Big Deal About Small Outages.)

Less than 1 percent of U-verse customers (there were 7.4 million of them at the end of the third quarter of 2012) were affected by the outage, the company's statement said, acknowledging that that's still "too many." She also said the cause of the outage was "related to a software upgrade."

On Wednesday, AT&T told the Houston Chronicle that the outage was also linked to a problem with the U-verse "server complex."

AT&T is scheduled to report fourth-quarter results Thursday afternoon.

— Jeff Baumgartner, Site Editor, Light Reading Cable