PDA Street and Bargain PDA have stories on the possible future use of the Nintendo DS as a PDA device (something that the company would have planned from the start, as the next gameboy advance would be the 'pure gaming handheld machine').
Since the hardcore audiences are more likely to adopt the next gameboy advance, the innovative titles made for DS will reach, apparently, a more casual / nongamer share of the market.
Interestingly, if successful, Nintendo will sell PDAs that are actually gaming devices. On the other hand, the Zodiac, Tapwave's PDA / gaming handheld hybrid, will lose its unique selling point.
It's a shame how Zodiac is not popular at all as a gaming machine. It has widescreen, 3D graphics, it can play mp3s and videos, it can be used with a stylus... It is more expensive then most competitors (around U$ 350), but with a better game library, it could have been more successfull among gamers and attract a larger audience.
Plus, it could be a great option for small developers too.