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There are two types of telephones  commonly in use  around the world,  pulse
 (rotary dial), and touch-tone (buttons). The two systems of dialing operate
 quite differently from each other.
Pulse dialling actually hangs-up your phone for 0.05 seconds for each number
 in each digit.   For example, if you are dialling the number 6,  your phone
 briefly hangs-up  six times in rapid succession.   This short hangup is too
 brief to actually disconnect you,  but it is just long enough for the phone
 company's switching equipment to notice. One problem with pulse dialling is
 that the higher the digit,  the longer it takes to dial.   The digit 1 only
 takes a tenth of a second to dial, whereas 0 takes an entire second to send
 ten pulses.
Touch-tone dialling uses Dual-Tone MultiFrequency (DTMF)   Hz  1209 1336 1633
 to signal what digit was  dialed.   This means that the
 phone generates two tones (or notes),  one representing   697   1    2    3
 the row of the digit, the other representing the column
 (see the chart).   For example, if you are dialling the   770   4    5    6
 digit 6,  your phone would generate a 770 Hz tone and a
 1633 Hz tone and simultaneously send them both down the   852   7    8    9
 line.   The phone company's  switching equipment  needs
 only a tenth of a second  to figure out which two tones   941   *    0    #
 are present, and thus what digit was dialed.
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