The send, end, and/or push-to-talk functions of a combination cellular telephone/two-way radio, are controlled with a single button on a hands-free device having a cable attached to the button, a microphone, and an earpiece. The button is pressed to instruct the cellular telephone/two-way radio to transmit in a half-duplex communications mode for a two-way radio conversation. The user speaks while continuing to press the button, to transmit the user's words in the two-way radio conversation. Next, the user releases the button, to instruct the cellular telephone/two-way radio to cease transmitting, to permit the user to hear words transmitted by the other party to the two-way radio conversation. Additionally, in some examples the user may answer an incoming cellular telephone call by pressing the button used during the two-way radio conversation, to instruct the cellular telephone/two-way radio to establish communications for a full duplex cellular telephone conversation.