Communication between ships or stations with line of sight is conducted using communication masers (enterprising pirates will conceal their anti-ship weapons as comms masers). Inter-system communication is normally handled by courier ships, or in the case of exceptionally rich individuals, automated message pods fired from a moon-side mass accelerator/wave inception system. This is coincidentally also how a lot of freight is handled, particularly by the mining dynasties in their family ships in the Halo and Kuiper belts, who tends to just point their cargo pods at Jupiter or Saturn and let them rip.