Well, you need to be jailbroken with Cydia, but that will void your warranty. Also, there is not an emulator for the DS yet on the iPhone, but I've seen footage of one (Doesn't work very well/probably fake). Also, emulators are illegal.
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http://www.racketboy.com/retro/nintendo/nes/2008/03/best-nes-emulator-for-nintendo-ds-nesds.html
check the settings of the emulator, there might be a setting for that, otherwise you'll have to buy the game.
no get a life.
I don't know. But you can play it in a Nintendo DS Emulator.
No, but it is illegal to download ROMs, BIOS files or any unauthorized copies of DS games.