While surfing around and reading news I discovered an interesting project named fonie. To make it short it offers an voice tel within your browser. You dont need to install a plugin or other software. From the technology part what are they doing ? Fonie.de is using adobe flash to grant access to your microphone and webcam for their webbrowser video-telephony.
If you want to test it just visit their homepage and start a new call. You will receive a link that you can send to your friend … The sound quality is not the best but I believe that this will be changed soon if a big Investor will help them