Rumored details are scarce, but judging from the image, the phone will come with a large touchscreen, a Genius button, a likely camera button, possible front facing camera, trackpad, and finally: physical home, menu, and back keys.
AndroidGuys did some close analyzing of the picture from Android Central and believe that the phone may also have ambient light and proximity sensors.
No inside specs to be mentioned at this moment, but it does look interesting. What's more judging from all the educated guesses surrounding the HTC Vanguard, and the HTC G1 Blaze, we may be talking about two separate phones here, with this phone above being the HSPA+ phone.
Of course, this all could be some hoax. Android Central want this tip to be true, but admit that the image has them feeling as though it is "more than a fan-rendered mockup (though that's still a possibility)."
There is not really any other option besides waiting and discovering what T-Mobile has to say, or until the next leak comes out.
Image from Android Central