Not yet. And the device has only been out for four days, so it'll be a while before we start seeing hacks. And voip would be something that Apple would be out to destroy saying that would make direct iPhone competition.
There's no microphone on the touch, and the microphone on the iPhone's headset will not work with it either.
Maybe someone will make a microphone work with the 30pin connector eventually.
Edit: or maybe the iPhone headset will work, I dunno. I just assumed Apple would disable it on the touch.
No, you were correct. The headset on the iPhone uses a recessed jack to accommodate for the mic. Obviously, this was not passed onto the iPod touch... since that's just asking for people to develop a voip client.