This is a couple of days old at the moment, so if anyone has a story countering this or showing that the breach was a prank or simply just a false claim, please post it below in the comments.

Early reports indicate that hackers have penetrated the T-Mobile U.S. network and stolen proprietary operating data, customer databases and financial records. According to a post on insecure.org, the hackers have claimed to be auctioning the pilfered data to the highest bidder. T-Mobile competitors, they say, turned them down.

There are no details as to how the hackers achieved the breach, but they did post code to show that they did penetrate the T-Mobile network.

T-Mobile was the target of a masssive 2005 hack, in which Nicholas Jacobsen was charged with unauthorized network access by the U.S. Secret Service. According to published reports, Jacobsen had access to all the information about T-Mobile's 16 million U.S. subscribers.

T-Mobile subscribers are also the frequent target of e-mail and text messaging phishing scams.

UPDATE: There is no mention of a security breach or incident on T-Mobile's Web site. We spoke with T-Mobile Saturday night, and they were unaware of the reported incident. They were looking into it, but stil have not provided a formal response.
http://blogs.channelinsider.com/secu...le_breach.html

T-mobile has responded with the following statement.

"The protection of our customers' information, and the safety and security of our systems, is absolutely paramount at T-Mobile. Regarding the recent claim, we are fully investigating the matter. As is our standard practice, if there is any evidence that customer information has been compromised, we would inform those affected as soon as possible."