Communication

There are several ways for people to communicate large distances. People on the same planet can use EM signals or fibre optic cable, akin to communication on Earth. For longer distances, EM signals can be used. These signals travel at the speed of light, and so information can be transmitted to other planets within minutes or hours. The signal does weaken over distance, however. Another possible benefit of EM signals is that they can be intercepted by any receiver, which makes them ideal for distress communications. These EM signals can be encrypted, of course, and these encryptions can be cracked. 
The other method of communication is via quantum entanglement. This is a physics phenomenon, wherein two particles can be linked together in a certain way so that their states remain identical, no matter how far apart they are separated. Two communication devices can establish an entanglement link, by entering in each other's codes. This allows calls in real time, regardless of distance. Compared to EM signals, it is much faster, and impossible to intercept. However it is only possible when both devices have the entanglement codes of the other device, and so cannot be used as a distress signal.