That is not possible. You can transfer DSiWare games from DSi to 3DS, but not the other way around.
No.
No, you can't.
The Nintendo 3DS will be able to play Nintendo DS and DSi games but games published for the Nintendo 3DS will not be compatible with those systems.
No, you can't.
No because the 3ds game is to big to put in a dsi
No, the DSi is only compatible with DSiWare.
You buy ds or 3ds games and then put them in your 3ds.
Only in the original Nintendo DS and the Nintendo DS Lite. DSi, DSi XL and 3DS do not have a slot to put GBA games into.
It won't fit in a DS or a DSi, there is a tab on the 3DS game to stop it.
No, because Nintendo put a little stub on the 3DS cartridges, so when you put in the DS slot it doesn't fit. Also, if the stub wasn't there, the DS wouldn't be able to handle the 3DS' graphics and wont load the 3D effect of 3DS games on a standard DS or even DSi.
No, there is no way to do so. The 3DS will support Miis, though.
Gameboy color/colour games do not work on the following systems (this is because there is no slot to put it in, however on the Nintendo 3DS you can download some GBA/GBC/GB games):Nintendo DSNintendo DSiNintendo DSi/XLNintendo 3DS