TechRadar sent an inquiry to Skype about the possibility of its VOIP telephone service appearing on the Nintendo DSi. While we'd love to tell you that the Skype rep responded with a concrete "yes," we can at least say that the representative didn't totally shut TechRadar down. In fact, the wording of the boilerplate response suggested that there's no reason the service wouldn't spread to the DS platform.
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.