Is anyone using GroupWise Mobile Server/Intellisync client with an AT&T Tilt phone?

I'm having the user hit our GMS server's /install link via the phone's browser. When I do that on my phone, I get Windows Mobile 5 SmartPhone Edition as my only installation choice. His phone however is running Windows Mobile 6 Professional. It looks to me like GMS is unable to determine what OS his phone is running, and is therefore giving ALL the choices to pick from - Blackberry, Palm, Pocket PC, etc.

Which one (if any) works with this device? He's tried the Pocket PC and the SmartPhone links. Both are presenting him with "where do you want to extract these files" and showing him the contents of the .cab file - the cabsetup.999, 00000pkg.00* files, etc.