SAN ANTONIO (AP) — Customers of AT&T Inc.'s premium television service, U-verse, were hit with outages nationwide on Sunday, the company has confirmed.

The problems started everywhere early Sunday morning and, while AT&T was able to restore some local channels and popular cable news and sports networks within a few hours, full service wasn't restored until Sunday night, AT&T spokesman Michael Coe said Monday. Some customers had to reboot their cable box to get service restored.

The cause of the disruption remains under investigation, Coe said. He said the company was also reviewing its customer service policies after some users complained on Internet forums that they were unable to get customer service help when they needed it Sunday.

The outage is the latest glitch—and among the highest-profile—for U-verse, which uses a relatively untested technology to deliver television over a high-speed Internet connection.

The early rollout of the product, which AT&T is hoping will help it fend off cable companies now selling phone service, was plagued by delays and questions about the software, provided primarily by Microsoft Corp.

Since earlier this year, however, AT&T had been ramping up rollout and installations, with 100,000 customers signed up by September. It's now available in 33 markets. The service had just 3,000 customers at the end of 2006.

AT&T sees U-verse as a critical component in its effort to slow desertions by traditional phone customers and to win new customers with features that will blend and overlap television, wireless devices and computers.

AT&T is scheduled to release earnings for the third quarter on Tuesday