The Astrophone was a piece of technology in-use by the Office of Space Affairs on Earth. Their offices, space stations, space ships, and vehicles were equipped with this device which allowed audio communications over great distances. The Astrophone could be used in conjunction with the Visiograph to have visual and auditory communications. There was even a portable version of the device.
The astrophone was handy - when it worked. It could easilly be disabled by villians, and did have a range limit. Some do appear to be more powerful than others, as Rocky contacted Space Affair Headquarters to have them use their more powerful astrophone in Inferno in Space. The astrophone could be overpowered by cosmic radiation (Cold Sun).
Nearly every race uses one version or another of the astrophone. You can see the various designs that each race uses over the course of the Rocky Jones series.