How Does Push to Talk Work?

Overview and History
Push to Talk, often abbreviated as PTT, refers to any two-way communication where a user has to push a button to talk, and then release it to listen to the other party. In modern usage, it refers to a feature on mobile phones that allows users to simulate a 2 way radio communication. Cellular Push to Talk also allows groups of people to establish a simulated radio dispatch between all members of the predetermined group without making everyone call in.
Cellular Push to Talk came to be when Nextel Communications, named FleetCall at the time, began purchasing specialized mobile radio frequencies across the country. These frequencies were primarily used for truck and cab dispatch, but as the technology grew, it allowed the cells to “speak” to each other and enabled the growth of the network beyond just a small region. When Nextel grew into a nationwide carrier, it kept part of its radio past in the form of Push to Talk over its network.
Functionality
Push to Talk establishes a half-duplex method of communication, meaning only one person can transmit at a time. Normal cellular calls establish a full-duplex connection by making two different connections between the tower and the handset at two different frequencies, one for communication to the handset, and one for communication from the handset.
Push to Talk only establishes one connection, thus when someone is speaking, the other parties cannot. The user can change between talking and listening by either holding or releasing a button on the device.
To use the service, the user would first enter the number of the person or group that they wish to connect to, and push the button to establish the connection. The tower recognizes the connection and connects through the network to the intended recipient. The recipient is then notified by their phone that they have an incoming PTT connection and if they answer, a connection is established until they disconnect or lose their signal.
At this point, whoever pushes the button is the speaker, and all others on the connection are listening only. If someone pushes the button while another person is speaking, they will get an error sound from their phone and will still have to wait until the line is open to push the button and talk.