Star Hero: Noble Ideals
Transmission via tachyon waves is used galaxy-wide due to its advantages in range and speed over other known methods. Personal comm units generally have a planetary range on their own, but can use ship, satellite, or ground relays to reach across the galaxy at near-instantaneous speed. Due to the nature of tachyon transmissions, directional tracking is generally difficult.
Note that while directional tracking is difficult, use of relays can certainly be monitored. Skilled operators can attempt to conceal or obscure their communications; and skilled monitors can overcome this!