What is ISDN? ISDN, which stands for integrated services digital network, is a system of digitizing phone networks which has been in the works for over a decade. This system allows audio, video, and text data to be transmitted simultaneously across the world using end-to-end digital connectivity. The original telephone system used analog signals to transmit a signal across telephone wires. The voice was carried by modulating an electric current with a waveform from a microphone. The receiving end would then vibrate a speaker coil for the sound to travel back to the ear through the air. Most telephones today s