Research in Motion, maker of the ubiquitous BlackBerry handheld device, reported a "critical severity" outage in its email service on Monday afternoon.

"This is an emergency notification regarding the current BlackBerry Infrastructure outage," R.I.M. support account manager Bryan Simpson said in an email.

Millions of users in the United States were affected, regardless of provider. Users reported BlackBerry service failing at about 3 p.m. New York time.

A spokesman for AT&T said nearly four hours later that service had been restored, according to Bloomberg News.

"Obviously, the important thing is that it was fully restored quickly," Jim Balsillie, co-chief executive of Research In Motion, said today in an interview with Bloomberg Television from Barcelona. "It was pretty focused and isolated and we recovered well."

This is not the first time the company has had a major BlackBerry service crash. In April 2007, BlackBerry email service across North America failed, leaving thousands of users unable to send and receive emails.

At the time of last year's crash, Balsillie said that such disruptions were "very rare" and pledged that the company would prevent such a service failure from happening again.

Unfortunately for Balsillie and R.I.M., the company appears to have been unable to do so.

The Wall Street Journal points out that "both outages point to vulnerabilities in R.I.M.'s delivery model, which has also been one of the secrets of its success."

BlackBerry emails are routed through a network operating center, where they are encrypted and sent out through the cellular-provider networks.

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