Maybe now they are communicating with each other throughout Our Universe. Even if USA agencies may have listened to some communications among ETs, it may be that they cannot translate what they are hearing (unlike the Hollywood fiction of the movie Contact). It may be that the USA listeners don't even recognize that the signals are communications, sort of like the Western Native American Indians who may have had no idea what messages were going over the telgraph lines through their homeland.
To carry information over long distances, they would use Electromagnetic Photons.
To carry more information, they would use high-frequency Gamma Rays.
To be energy-efficient in transmitting information from point to point within the Milky Way, they would use Gamma Ray Beams that are Gravitationally Focussed by a star near the point of origin.
The Pogo cartoon at the top of this page was scanned from page xvi of Intelligent Life in the Universe, by Carl Sagan and I. S. Sklovskii (Holden-Day 1966), which is an English translation, expanded with some commentary, by Carl Sagan of the book Vslennaia, Zhizn, Razum (Universe, Life, Mind) by Iosef Shmuelovich Shklovskii published in Moscow in 1963, parts of which were serialized in Komsomolskaya Pravda and published in Priroda.