The term PTT radios (push-to-talk radio) also known by a few other names like POC (Push over cellular) has lately become the new buzzword in the communications industry.
The main difference between a two-way radio as we know it and a PTT radio is that the PTT radio uses cellular signals to connect to a network and make a call, whereas the normal two-way radio is frequency dependent. a PTT radio therefore contains a sim-card just like the one in your cellular telephone. The sim-card makes use of the data connections on the cellular networks instead of the lines normally used for making a telephone call. By making use of the data transmissions the radio is therefore able to allow users to connect quickly and cheaply because the voice communication now only uses small fractions of data at a time.