In fact, it is so easy to use that I was simply able to drop it over the top of the drupal-phone.tpl.php template file in DruCall, tweak the drucall.js module to call JSCommManager.init() and DruCall is now the first solid implementation of JSCommunicator.
Before pushing this new version out to the community, it is undergoing some testing / baptism by fire. Lumicall recently announced free calling from desktop browser to mobile app powered by JsSIP's "tryit" demo code.
The DruCall module has now been deployed here on the Lumicall website as a parallel solution to access the same free calling service.
JSCommunicator comes from server-side developers rather than web developers. It provides a solid communications tool but it doesn't look great.
The project aims to be a HTML fragment that can drop into just about any page on any web site, so it has been designed to be as raw as possible and allow the styling of the existing web site to influence it. Nonetheless, it could still look a little bit nicer and I would be delighted to see any CSS-based skins that people may develop to enhance it.