Feb. 11 (Bloomberg) -- A network breakdown disrupted BlackBerry e-mail service for about 8 million customers in North America, the biggest failure for Research in Motion Inc. in 10 months.

AT&T, the largest U.S. phone company and a provider of BlackBerry service, learned of the interruption from Research In Motion at 3:30 p.m. New York time, AT&T spokesman Fletcher Cook, said in an interview today. Verizon Wireless, the No. 2 mobile carrier, also confirmed the disruption.

Business people -- from hedge-fund managers and analysts to lawyers -- rely on the BlackBerry for e-mail access, news and stock quotes, and increasingly for information such as train schedules. Research In Motion needs to fix the problem quickly to prevent rivals from capitalizing on the outage, said Morgan Keegan & Co. analyst Tavis McCourt, who lost his BlackBerry service in Nashville, Tennessee.

``I'd need to catch up with the story, but I've lost my access,'' said McCourt, who advises investors to hold on to the stock and doesn't own any. ``If it drags on it becomes a headache.''

A data service interruption is causing ``intermittent service delays'' in North America, Research In Motion said in an e-mailed statement. The company, based in Waterloo, Ontario, is working to fix the problem and will provide an update as soon as possible. Users won't be able to send or receive messages or browse the Web, Research In Motion said in an e-mail to customers today.

Research In Motion reported that the problem has been fixed, AT&T spokesman Mark Siegel said at 6:45 p.m. New York time. Both AT&T and Verizon Wireless said all North American carriers were affected.

Shares Fall

Research In Motion dropped $1.12 to $93.35 in extended trading. The stock gained $4.76 to $94.47 at 4 p.m. New York time on the Nasdaq Stock Market. The shares have more than doubled in the past 12 months.

Last year, a malfunction in newly installed software led to disruptions in the BlackBerry service, shutting off Internet access across North America. In that incident, a switch to a backup system led to further delays.

Research In Motion has more than two-thirds of its 12 million BlackBerry subscribers in North America.

Service interruptions raise investor concern that customers will look to rival companies, analysts such as Nomura International Plc's Richard Windsor have said. Nokia Oyj and Motorola Inc. introduced new devices and have acquired e-mail service providers in the past three years to challenge Research In Motion.

AT&T, Verizon Wireless and other phone companies pay Research In Motion for each subscriber that uses BlackBerry e- mail. The fee is about $6 a month, estimates Goldman, Sachs & Co. analyst Brantley Thompson.

To contact the reporter on this story: Ville Heiskanen in New York at vheiskanen@bloomberg.net; Crayton Harrison in Dallas at tharrison5@bloomberg.net

Last Updated: February 11, 2008 19:12 EST