AT&T likes to rebrand phones as their own. Verizon does the same and this often confuses consumers because they fail to recognize key smartphone manufacturers like HTC. They may recognize names like Samsung and Motorola, but they don't know HTC.
The AT&T Pure is really an HTC Touch Diamond2 that's been rebranded. The Touch Diamond2 is a great smartphone for people who don't mind the Windows Mobile 6.5 operating system and who also don't need a hardware keyboard. If you can live with an on-screen keyboard (similar to the one found on the Apple iPhone), then you should be quite content with this device - as long as you're familiar with Windows Mobile.
The AT&T Tilt2 is a rebranded HTC Touch Pro2. This is a thicker smartphone that has a slide-out QWERTY keyboard. I love my Verizon Touch Pro2 and I welcome the thicker device for the hardware keyboard.
One of the biggest benefits of Windows Mobile right now is the fact that there's a plethora of medical software for Windows Mobile 6.5, 6.1, 6.0, and even older versions of Windows Mobile/Pocket PC/etc.