Existing phone systems are driven by a very reliable but somewhat inefficient method for connecting calls called circuit switching.
Circuit switching is a very basic concept when a call is made between two parties, the connection is maintained for the duration of the call. Because you're connecting two points in both directions, the connection is called a circuit. This is the foundation of the Public Switched Telephone Network (PSTN).
Talk for 10 minutes using PSTN during this time, the circuit is continuously open between the two phones. Your voice is digitized, and your voice along with thousands of others can be combined onto a single fiber optic cable for much of the journey (there's still a dedicated piece of copper wire going into your house, though).
A packet-switched phone network is the alternative to circuit switching packet switching opens a brief connection -- just long enough to send a small chunk of data, called a packet, from one system to another.Packet switching is very efficient the network route the packets along the least congested and cheapest lines.