Ansible

From Orson Scott Card Wiki

The Philotic Parallax Instantaneous Communicator - a device used for instantaneous interstellar communication. The term ansible someone 'dug out of an old book somewhere', and it caught on.

The ansible uses the Philotic effect to "vibrate" philiotes, which consequently shows the same vibration on a philotic counterpart, no matter how far away it is. The connection allows communication to be instantaneous throughout interstellar space, which is how the Hundred Worlds were able to interact, even though the colonies were light-years apart.