An article from WiFiNetNews.com indicates that T-Mobile will be running both networks in tandem during the interim period and will be rolling it into their new connection manager software (available only for Windows now, but they've promised Macintosh and PocketPC support in the future).
I'm not surprised about this, because it makes their new iPaq offering a lot more interesting from a VOIP perspective. Imagine if your phone "roamed" onto a hotspot and then you had to open a browser and log in to get your VOIP access... not good.
T-Mobile claims their implementation will work out-of-the-box on Macintoshes and Windows machines running XP and recent CE versions.
It is unclear as to whether a new network name is required to use 802.1X.