According to the representative, Skype's growth strategy "includes extending the Skype infrastructure and platform to bring Skype functionality wherever, whenever, and on whatever device or site people choose to use it." Currently, that includes computers, some smartphones, and, of course, the PSP. As for the DSi, "Whilst we can't comment on any future plans to bring Skype to Nintendo's DSi, it would technically be possible."
Of course, DS homebrew enthusiasts have known for a couple of years that it's possible. But the DSi Shop makes it seem more likely to happen in an official capacity.