Diamondback Jay
Psalms 23:1
Does anyone know what this is? Can people call you on it?
Yeah you have to have the hardware for it (usually a USB phone).
It's has a proprietary protocol that doesn't follow the VoIP standard which is really, really stupid. I've heard that if you don't know what you're doing you can inadvertently become a super node with people piggy backing off your connection and basically bring your internet connection down to a crawl
Also it doesn't support Windows Vista and they haven't even said they plan on doing it.
If you want VoIP I would pick this as a last, last resort