A two-way radio is a radio that can both transmit and receive (a transceiver), unlike a broadcast receiver which only receives content. Two-way radios are available in mobile, stationary base and hand-held portable configurations. Hand-held radios are often called walkie-talkies or handie-talkies. A push-to-talk or Press To Transmit button is often present to activate the transmitter. A mobile phone or cellular telephone is an example of a two-way radio that both transmits and receives at the same time (or full-duplex). It uses two different radio frequencies to carry the two directions of the conversation simultaneously.