Try and find some sort of thin, pointy object, like a bobby pin, stick that in there and try and pull out the paper towel. It MIGHT work depending on how hard it's jammed in there. But hey, at least it's just your stylus slot. I once got something stuck in my GBA's game slot. Couldn't really play anything for a while. -_-
Hora kimi no sugu me no mae ni iru, sono namae wo saa, itte goran kono boku no namae wo! eFTo
since everybody is suggesting the same thing i'll give a weird alternative in case they don't work, stick a straw in and suck hard to get it on the end and pull it out maybe? xD
@Takis Teh Greek: I don't think I'ma open my DSi, never have, never will. I don't want to mess up anything >_> And I don't think my DSi would like that. (I treat it like a child)