How does the walkie-talkie feature on a Nextel phone work?

...Nextel is unique among service providers because it has an entirely separate special cellular network that has its own frequencies and equipment in addition to the normal cell network shared with other providers. This network is based on Motorola's Integrated Digital Enhanced Network (iDEN) and makes Direct Connect possible. It uses the 800 MHz portion of the radio spectrum assigned to specialized mobile radio (SMR) service. Nextel has purchased a large segment of these frequencies in a significant number of the national and international cellular service markets... ...When you make a Direct Connect call to someone, here's what happens: * You hit the Direct Connect button, which is configured with the number(s) of the person (or group) you are calling. * Your phone establishes a session with the Nextel iDEN-based network. * The network determines that this is a dispatch call (Direct Connect) instead of an interconnect call (a normal cell phone call). * The network then determines if it is a one-to-one or a group call. If it is a group call, the network duplicates the digital voice packets for each phone in the group. * The network routes the packets to the phone (or phones) of the person (or group) you are calling. * Their phone alerts them that they have a Direct Connect call. * They answer the call by pressing the Talk button. Whoever is pushing the button, whether a one-to-one or group call, is the speaker. * The call is completed and everyone disconnects...

How does the walkie-talkie feature on a Nextel phone work?