The PSP has voice-over-IP software Skype, and hey, Skype is technically possible for the DSi. That doesn't mean because it's possible that the DSi is getting Skype.
A Skype representative told website TechRadar, "Whilst we can't comment on any future plans to bring Skype to Nintendo's DSi, it would technically be possible." (Whilst?)
This comes as Nintendo President Satoru Iwata stated that the Kyoto-based video-game company is not interested in entering the mobile phone market. Skype would be an easy way for Nintendo to sidestep that and still give the DSi added functionality.
When asked about Skype on the DSi, Nintendo told game site CVG: "We have no plans to release a Skype application for Nintendo DS or DSi." Maybe one day Nintendo will have plans and then you'll have Nintendo-approved Skype on your DSi.