Gizmo's gizmocall.com had a recent upgrade. You can place calls via a web browser. They previously had this, but required a download and Linux ccomputers were not supported. The new version is multi-platform and no download required. It even works on the N800! It also receives calls.

I think this is great since it allows you to still use voip on public AP's that have port blocking enabled such as Best Buy, etc.

www.gizmocall.com