Digital and Analogue phone systems:
phone systems are built on traditional copper wire. Audio or video signals are converted into electronic pulses, using analogue phones and phone equipment, so that it can be transferred along the network, and then converted back to audio or video at delivery point.
phone systems may or may not use copper wires - other technologies such as fibre optics are available to carry data. Audio and video signals are converted into binary code, or digital signals, using either specific phones or converters like gateways.
phone systems features are limited to transferring calls between extensions, hold, redial, mute and speed dial. Digital phone systems enjoy many more features such as music on hold, VOIP, presence, unified messaging, voicemail transcription to SMS, and CTI features such as click to dial and CRM integration.
phone systems are more versatile and allow many more users to share the same line. Even if digital systems enjoy cleared sound, analogue systems still have better sound clarity.