SIM...card...? The one that goes in phones? Half the size of the SD slot? I hope you're joking. Dude, I'm not trying to make you feel bad, not even trying to make fun of you (because you're getting enough of both by this point), but I'm very curious as to why you think it'd work? (probably be better for PM since it'd probably result in more smartass comments) I heard of a micro SD card falling in, and now this?
Anyway, I'd say your best bet is to call Nintendo for some support and maybe, if you're lucky, they'll provide a way for you to get it out (either have some sort of procedure for this sort of thing or send it back and they'll dissassemble it for you to retrieve the card).
If you're feeling even luckier you can try shaking/air-canning that thing out of there, but I took a look at the SD card slot and the holes look too fine of a fit to manage to get something as small as a micro SD card or a SIM card out of that console. If you can live without the card, work around it, because it's not as if it's really going to damage the system. Otherwise, as suggested, just call nintendo.
He could result to that if Nintendo doesn't help him, but it's best as a last resort. May wanna hold onto that warranty if there's another way around it. Then again, is there even a VOID sticker or device anywhere in the console?If you google something like 'Taking the wii apart' you should find some sites where people have... well.... taken the wii apart. Either study the pictures to see where the sd card slot opens up to or send a very nice, polite email to the people who took their wiis apart asking for advice.