The Dark Forces Team, famous HTC hackers, have been working for some time on adding USB Host, which allows USB periferals to be added to phones, to the HTC HD2.
Their effort has not been without success, but they want to move on to other things, and have decided to release what they have achieved so far.
The current solution supports the Human Interface Devices profile, meaning mice and keyboards can be added, and also USB Mass Storage, meaning hard drives and pen drives are supported. Â They warn that the implementation is still expirimental and a self-powered USB Hub or special cable may still be required.
If you are still sporting an old-style Windows Mobile 6.5 HTC HD2 and you like hacking, read more in the XDA-Dev thread here.
Thanks ele for the tip.