Quoting the thread I will link to below:

The Radio ROM is the software part of your device that is powering on/off and controlling your radio interfaces. This includes Bluetooth, 2G/3G Phone, WiFi, GPS..... And it also includes the OEMSBL (Radio BootLoader) and other device specific firmwares needed for using your radio interfaces and for interfacing them with the OS (Windows Mobile/Android).

To run Android on the HD2, you need at least radio 2.08.50.05. The latest radio's aren't always the better ones, it is advised to play around with a few and see which give you the least problems, and more battery life.

The HTC HD2 Master Radio Thread

http://forum.xda-developers.com/showthre...