Ansible

An ansible is a kind of fictional device or technology. Ansibles can communicate faster than light. It can send and receive messages to and from a corresponding device over any distance or obstacle whatsoever with no delay, even between star systems. As a name for such a device, the word "ansible" first appeared in a 1966 novel "Rocannon's World" by Ursula K. Le Guin The word shortened from "answerable." It allowed users to receive answers to their messages quickly, even over interstellar distances. 
In Le Guin's works.
Any ansible may be used to communicate through any other, by setting its coordinates to those of the receiving ansible. They have a limited bandwidth which only allows for at most a few hundred characters of text to be communicated in any transaction of a dialog session, and are attached to a keyboard and small display to perform text messaging.
Other writers.
Many other writers have ansibles in their fiction. Examples include: