WPCentral posted a story that a Windows Phone Mango ROM has been released for HTC HD2

For those of you still running an HTC HD2 aka the device the runs everything, you'll be pleased to know you can now load Windows Phone Mango 7720 onto that bad boy, making it a true, honest to Ballmer Windows Phone (it makes your SD card act as a single partition).
We're not gonna lie, the number of steps, folder moves, flashing and technique here is no small feat. You'll want to take your time, print out those directions and cross your fingers you don't miss anything.

  Windows Phone Mango ROM released for HTC HD2