T-Mobile has posted a small announcement within the support section of the website, on the HTC HD7 support page, that asks customers not to contact the carrier with regards to the Mango update for the HD7. They state that it's "coming" and is ready for deployment, customers will receive a notification soon (don't pay too much attention to the 2 weeks time frame provided).
The link for the installation instructions takes us to a Zune update walkthrough page. It was published in August this year so it's definitely for Mango. There you go T-Mobile Windows Phone users, some hope for you and light at the end of the tunnel.
Source: T-Mobile, thanks Nick for the heads up!