PSP can now play more Gameboy games than DS
 

http://forums.ps2dev.org/viewtopic.php?t=1648

Pretty hot I would say. Just run it off the memory card.

Also, you CAN play GB games on a DS through a GBA flash cart, but you get a mem card with a PSP at the mo anyways, so it's easier to get hold of ;)

This will be interesting once they get the ROMS to work 100%.

(Sound)

'Cept there's already hardware that allows this (You mentioned) and the capacity to play ROMs...Oh well...