DruCall (the WebRTC module for Drupal) is being updated to use JSCommunicator from http://jscommunicator.org
I've deployed the new DruCall as an alternative to the existing service for free calls to Lumicall:
http://www.lumicall.org/drucall (new, based on DruCall/JSCommunicator)
http://webrtc.lumicall.org (existing service, based on tryit.jssip.net)
If it works in your browser, you should be able to dial any phone that has Lumicall installed - just dial the number in E.164 format, e.g. +447771231234 for a UK number.
I'd be interested in any feedback about this. It would also be really useful to find somebody who is good with CSS who can help make JSCommunicator look a little bit more pretty.