They're all basically the same phone, but they're offered by 4 different US carriers. The software customizations are different as are the 3G bands (for T-Mobile vs. AT&T). The Sprint and Verizon versions use a different network technology called CDMA.
AT&T likes to be different, so they went with "Tilt2" instead of "Touch Pro2" for the name .
-------------------- Lisa Gade Editor in Chief, MobileTechReview