A method for decoding a DTMF tone which includes collecting the width of serial signals by measuring the time interval between zero-crossing points within a predetermined time; counting within the predetermined time the number of signal zero-crossing points; performing interpolation on the data produced by the collecting and counting steps with a Fourier transform; identifying a first frequency that has the strongest magnitude from the resulting data; and calculating the lower frequency of the tone being decoded by subtracting the first frequency from the average frequency of the digitized signal. The invention also includes apparatus that utilizes a zero-crossing detector for receiving a DTMF tone to be decoded and producing a digitized output; apparatus for collecting the width of serial signals by measuring the time interval between zero-crossing points within a predetermined time; apparatus for counting within the predetermined time the number of signal zero-crossing points; apparatus for performing interpolation on the data produced by the collecting and counting steps with a Fourier transform; apparatus for identifying a first frequency that has the strongest magnitude from the resulting data; and apparatus for calculating the lower frequency of the tone being decoded by subtracting the first frequency from the average frequency of the digitized signal.