Since the earliest days of space travel, and stretching back even further to the naval vessels of the 20th century, ships have had 'communications arrays'. In their most basic form these can be as simple as an RF antenna, but in the 24th century even the smallest shuttle will have at least some sort of communications device capable of transmitting over an area only dreamed of in the 21st century.
A communications array is a varied network of signal processors, transmitting and receiving antennas (containing subspace amplifiers) designed to enhance or support communications through interstellar space. These arrays can handle a wide selection of signals, from voice and digital to the current holographic methods. Communication arrays are often interconnected with sensor arrays and can be deployed as platforms in space, as essential components of starships, or in larger installations on planets. (Memory Alpha) Since subspace is the preferred medium on which signals are sent by nearly all major galactic powers, arrays are usually attuned to tansmit and receive in that manner. Exterior communication arrays handle ship-to-ship, ship-to-planet, and deep-space signals. A seperate but readily linked internal communications network is reponsible for intraship messages.
Most starships or facilities will be equipped with both a primary communications array and at least one redundant backup array too.