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The differences between Rotary and Dual Tone Multi-frequency (DTMF are with Rotary relates to rotation, part that rotates around and axis. Rotary are one of the oldest phones used since the 1920’s and they are still used by some. For every number dial around the rotary it turns on and off the switch at the phone company. As for DTMF which is suppose to replace rotary. It uses audio signals which generate when one presses a button on a touch tone phone. The audio tones send a signal to the phone company. Each key generates two tones of specific frequencies. One is a high frequency and the other is a low frequency. The differences between Private Branch Exchange (PB