Yeah, Facetime video seems to work well compared to others. It was a bit hard to explain to a couple of business guys, that "no, we are unlikely to get anything close to Facetime quality with WebRTC solution, but I don't know why."
You could try writing a FaceTime dara packet wrapper/unwrapper, which packs your application data into FaceTime video/audio packets, and unpacks it at the receiving end. If the carriers shape FaceTime traffic differently, it should be possible to establish whether this is the case, by emulating a FaceTime connection, as far as I can see. The content is encrypted, so I don't think they can shape traffic based on anything else than headers.
