I used "Freedom Universal Bluetooth Folding Keyboard 2" and I think it worked without hassle because I had kernel-power installed, but I'm not sure if that's the case with the default kernel.

I brought this model in 2007 (in the palm winmo days) and they don't seem to sell this model anymore on their website (but the Freedom Pro keyboard looks like its iteration)

my experience with using the n900 with the tv was mostly me wishing I had a BT mouse to easily navigate with (everytime I had to look back at the n900's screen to click on something, it left me thinking "why don't I just look at the n900?") so I was thinking about getting something like this but I have no clue if this will even work
edit: looks like you mentioned that in your first post