7   6   5   4   3   2   1   0   7   6   5   4   3   2   1   0   7   6   5   4   3   2   1   0   7   6   5   4   3   2   1   0
   +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
00 | Length                        | Digit 0       | Digit 1       | Digit 2       | Digit 3       | Digit 4       | Digit 5       |
   +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
04 | Digit 6       |  Digit 7      | Digit 8       | Digit 9       | Digit 10      | Digit 11      | Digit 12      | Digit 13      |
   +---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
08 | Digit 14      | Digit 15      |
   +---+---+---+---+---+---+---+---+

Where:
  - Length: Specifies the number of DTMF digits.
  - digits: 0=0, ..., 9=9, 10=a, ..., 13=d, 14=*, 15=#