The next generation Windows Mobile 2005 for Pocket PC OS beta version has been leaked for HTC Himalaya (T-Mobile MDA II, o2 XDA II, Qtek 2020). Rumours has it that it also works with HTC Magaician platform.
I downloaded the ROM image along with ActiveSync 4.0 beta but will decide later if its worth installing on my imate JAM.
You can get the ROM image here. Beware though, initial assessment by users are its very buggy and cannot sync via USB.