Only in Canada and Mexico, unfortunately, but this is not new.
http://www.t-mobile.com/Internationa..._RoamWorldwide
Unless they've just changed something, the page you pointed to was about their international calling rates -- i.e., how much it costs to call these places from the U.S. I certainly wish they'd enable roaming, at the very minimum, on other TMO networks, but my U.S. card presently won't roam in Germany, and you'd think it would work in the T-Mobile homeland if it would work anywhere. Oh well...