What's the reason for starting a new project when you could build on existing ones like Ekiga instead?
Ekiga is great, I actually prefer it to skype, as I can more easily set video/audio quality and it uses an open and standard protocol. They have binaries for any major linux distro , mac and windows, and it's fairly easy to compile from source if needed. The NAT traversal improved tremendously by the transparently use of stun, no configuration necessary. Give me my SIP IPv6 address and ekiga would work just fine for…
Don't forget that Skype's UX is only one fraction of why people like or don't like Skype. The codec they use is often vastly superior for "normal people" situations than even commercial SIP clients, or the WebEx-es of the world.
I don't doubt that the Skype network topology has something to do with it, but I am (perhaps erroneously) lumping those features together for the purposes of this discussion.