The guys on XDA-developers have stumbled upon a newly leaked ROM/Radio upgrade that unlocks the hidden RAM. It was originally discovered on XDA-China when a user posted a screenshot showing 576MB of RAM. Obviously, this leads to suspicion of fakery, but the Chinese post was made well before the specs for the U.S. HD2 were revealed. Some also believe that the displayed amount is just a misreading by the system and the readout is false.
One user, by the name of Brandi, has created a tool to test if the 576 figure is real or not. It essentially tries to use up available program memory and the results have been quite interesting. Apparently, he’s been able to use up 444MB of RAM, which is far more than he’d be able to pull off with the HD2 out of the box. Others are also confirming that the amount is, in fact, correct and custom ROMs (with the extra RAM enabled) are actually being released already.