tones:A String containing the DTMF codes to be transmitted to the recipient.
Specifying an empty string as the tones parameter clears the tone
buffer, aborting any currently queued tones. A "," character inserts
a two second delay.
duration: This value must be between 40 ms and 6000 ms (6 seconds).
The default is 100 ms.
interToneGap: The length of time, in milliseconds, to wait between tones.
The browser will enforce a minimum value of 30 ms (that is,
if you specify a lower value, 30 ms will be used instead);
the default is 70 ms.