Speaking of Windows Mobile 6, if you're really in a rush to get the new OS onto your T-Mobile Dash, hit up the link at the end of the post to grab it. It's the official T-Mobile release, so there shouldn't be any compatibility problems from having another device's ROM. And since it's the official release, it probably has the T-Mobile branding in there as well.
Reader Jimmie tells us that he installed it just fine and his phone hasn't been bricked. Nice work Jimbo. Now try and find the official MDA upgrade as well.