Found this thread on Fatwallet: http://www.fatwallet.com/forums/hot-deals/851965

I followed the instructions in the first post, and am keeping my fingers crossed.

If you read the whole thread, others have checked with TMO and this seems to be legit and just lowers your current bill by 10%. You can also sign up for new service this way... however the discount seems especially useful for existing TMO customers.