T-Mobile customer data on sale to highest bidder?

Crazy days, but this posting on the security mailing list Full Disclosure is pretty incredible.

Hello world,

The U.S. T-Mobile network predominately uses the GSM/GPRS/EDGE 1900 MHz frequency-band, making it the largest 1900 MHz network in the United States. Service is available in 98 of the 100 largest markets and 268 million potential customers.

Like Checkpoint Tmobile has been owned for some time. We have everything, their databases, confidental documents, scripts and programs from their servers, financial documents up to 2009.

We already contacted with their competitors and they didn't show interest in buying their data -probably because the mails got to the wrong people- so now we are offering them for the highest bidder.

Please only serious offers, don't waste our time.

Contact: pwnmobile_at_safe-mail.net

If it isn't a hoax then its not good. Not good at all. John Leyden at the Register has more details, including what appears to be confirmation from T-Mobile.