Facebook-Telephone is a project mainly written in JAVASCRIPT and RUBY, it's free.
Facebook Telephone
== Welcome to Facebook Telephone
http://apps.facebook.com/telephone
Facebook Telephone is a Facebook app that allows you to call your Facebook friends online. The application uses Voxeo's Phono SDK (http://labs.voxeo.com/phono) to deliver telephone quality communications in your browser without downloading or installing any third-party software. Best of all it's free!