This function sends DTMF tones over the phone line. A call must be active.
Parameter: Line
Type: Integer
Description: The phone line to access.
Parameter: Digits
Type: String
Description: A string of digits. Valid values are "1234567890#*"
Parameter: Duration
Type: Integer
Description: The time in milliseconds for each tone.
This parameter is ignored for the Hi-Phone device.
None.