Telepathy is the service doing the behind-the-scenes work for instant messaging using Empathy and a variety of other programs.
Telepathy is a flexible, modular communications framework that enables real-time communication via pluggable protocol backends. Telepathy is a communications service that can be accessed by many applications ("clients") simultaneously.
This allows any application to access presence information, request a communications channel (potentially handled by another client), or collaborate contact-to-contact. Telepathy provides protocol backends for most popular protocols, it also provides convenience libraries for GLib, Qt4 and Python to simplify using the API from applications.
Source:Telepathy Wiki