Two-Way Radio is a part of Lara's Gear in all of the Reboot games, Tomb Raider, Rise of the Tomb Raider, and Shadow of the Tomb Raider. In none of these games the player can actively use the radio, though it is seen in many cutscenes and Lara frequently uses it automatically in certain situations, too, e.g. in order to talk to her fellow shipmates on Yamatai or overhear the conversations of her Enemies in the vicinity.
Tomb Raider (2013)
The Two-Way Radio is found in the beginning of the level Signs of Life. Lara immediately uses it to try to find out what happened to the other expedition members of the Endurance, but she gets no answer. Later on, she hears Conrad Roth transmitting a SOS and finally can talk to him.
The radio is set to channel 34 throughout the game.
Rise of the Tomb Raider
In Syria, Lara does not have the radio with her.
Shadow of the Tomb Raider
Again, the radio is set to channel 34.