A recent Game Over column by Chris Morris builds up the possibility that Nintendo may be planning to include IM functionality in the upcoming Nintendo DS product:

"In an analyst report issued Tuesday, P.J. McNealy of American Technology Research said the upcoming Nintendo DS will offer Instant Messaging functionality. Rather than being offered nationally, though, the DS is more likely to offer local IM service, using free bandwidth with unlicensed RF spectrum (essentially, the same bandwidth that's used by two-way communication devices). Users would type messages on a touch screen using a stylus."

However, once you have implemented any sort of IM client, you could later on extend it -- either with a new public IM network, or through partnerships with other existing networks -- to provide universal access.

Of course, with so many rumors swirling around about the Nintendo DS -- multimedia capabilities (movies played from flashcards), wireless gaming (what exactly do they mean?) -- its hard to know where the speculation ends and hard facts begin.