Push to talk (PTT), is a means of instantaneous communication commonly employed in wireless cellular phone services that uses a button to switch a device from voice transmission mode to voice reception mode. The operation of phones used in this way is similar to "walkie talkie" use. PTT switches a phone from full duplex mode, where both parties can hear each other simultaneously, to half duplex mode, where only one party can speak at one time. Multiple parties to the conversation may also be included.
All major wireless carriers are rolling out versions of the service, which has been in wide use by Nextel (using the Integrated Digital Enhanced Network, or iDEN ) in the telecommunications and construction industries for years. These new versions of PTT, sometimes described as "Push To Talk over Cellular" (PoC), are based on 2.5G or 3G packet-switched networks using a form of VoIP based upon SIP and RTP protocols instead of iDEN. While current standards only allow users to talk to others within proprietary cell phone networks, future cooperation between companies and agreement on standards may allow interoperability between handsets on differing carriers.
Traditionally, a major attraction to consumers and businesses using PTT is the ability to communicate on-demand without using allotted minutes within a calling plan. This incentive may diminish as carriers adjust pricing structures to include PTT in data plans or in regular minute counts.
Early mobile telephony also used a form of PTT in the 1980s. Similar to operator-assisted landline telephone services of the early 20th century, mobile telephone users would press and hold a PTT button for several seconds to alert an operator. When the user released the button, an operator would then ask for the number the user wished to dial. The user would then transmit back and tell the operator the desired number, after which the operator would subsequently connect the wireless phone to the number desired.