T-Mobile has been planning to release their T-Mobile Dash Windows Mobile 6 upgrade on May 4th, but today the updater was released onto the web. It is not known who released the updater, but it has been confirmed that this is the final version set for release.
Microsoft and T-Mobile negotiated a software license upgrade, essentially, ensuring that all T-Mobile Dash owners would be able to upgrade to Windows Mobile 6 without paying an upgrade fee. This type of license upgrade has been offered in the past, most prominently when Microsoft encouraged device makers to upgrade from Pocket PC 2002 Phone Edition, to Windows Mobile 2003.
Because the software vouches as the shipping version, and because it includes a validated license upgrade, we are hosting the update for download. This is done in accordance with our Windows Mobile ROM policy. You can download the updater at the link below.
Update: The link above has been updated with the download from T-Mobile, as T-Mobile has officially released the upgrade.