Word on the street is that the Nintendo DSi may be getting a voice chat channel very soon. Nintendo has denied the rumor, but what would you expect? This is the company that offered up Wii Speak for the Wii.
Chatting on a DSi makes more sense. This sentence is what started the rumor:
To redeem a Nintendo DSi Download Ticket number, such as for the Nintendo DSi Speak Channel, enter the number off the Nintendo DSi Download Ticket in “Settings and Features” off of the main Nintendo DSi Shop page, then select “Nintendo DSi Download Ticket.