Subspace communication is a method of communication betweeb to points by sending the information through subspace.
Communication by cultures
Ancients
The Ancients developed subspace comunicators for use among their starships and their city-ships such as Atlantis. They also developed a Intergalactic communication device that link users extragalactically. (SG1: "Avalon") (SGA: "The Defiant One")
Asgard
The Asgard used less envasive subspace communicators, allowing them to communicate between galaxies as well. A platform would allow them to communicate with a hologram of one individual with a group of people. (SG1: "Thor's Chariot", "Red Sky", "Fail Safe", "Unnatural Selection")
Goa'uld
The Goa'uld used communication spheres to communicate between stars. It would allow them to communicate with each other visually. (SG1: "Within the Serpent's Grasp")
Replicators
The Replicators were linked through together through a subspace communication network, which is what allowed them to store information so quickly. It also allowed them to upload "immunities" to weapons that they encountered. (SG1: "New Order", "Gemini")