AT&T's wireless data networks in the Southeast and Midwest U.S. were down for several hours on Thursday, causing BlackBerry and iPhone users to be without data services.

The EDGE (Enhanced Data Rates for GSM Evolution) and UMTS (Universal Mobile Telecommunications System) services in those regions began having problems around 6:30 a.m. EST, said Mark Siegel, an AT&T spokesman. Voice calling was not affected, but people trying to use wireless data services may have had difficulty, he said.

The problem had been fixed by about 4 p.m. EST, he said. AT&T is still trying to identify the exact cause of the outage.

Several people reported in a BlackBerry newsgroup being unable to receive data to their handsets earlier in the day. A systems administrator in Kansas reported that BlackBerry devices there were displaying a message that said "data connection refused."

The iPhone runs on the EDGE network, so users of the phones, as well as any other mobile device that receives data over the EDGE or UMTS networks, may have had problems using data services during the outage.

In early 2007, Research In Motion implemented a software upgrade that caused its systems to crash, resulting in a BlackBerry service outage that started in the evening and lasted through the night. However, RIM said its infrastructure was operating normally on Thursday, meaning only the users on AT&T 's network were affected.

This story was updated on January 31, 2008