IGN has a blurb about DSpeak at e3. DSpeak let’s DS users make Voice-Over IP calls to other DS owners. The DS has an icon for a headset so perhaps we’ll see something soon. I’d propose a Skype/SIP/Vonage cartridge or prepaid cartridge and turn it in to a real phone. We’re getting more homebrew DS things, so who knows. Link.
DSpeak VOIP for Nintendo DS