[TELECOM Digest Editor's Note: I had a couple of Hayes Modems which
> could be switched between pulse and tone dialing, and you could set
> the 'speed' of the pulsing or the 'speed' of the tone signals. You
> could make both modes go quite fast; with tone dialing so fast that
> it was little more than just a single blip in your ear, and most
> times it would work quite well. Only on occassion the modem would
> give its short little blip or tone burst when dialing *before* the
> line was set up to allow it, and you would have to redial, but
> usually it worked okay. PAT]
Yes I remember those Hayes modems. We use to run the DTMF at 30ms on ESS switches, and 70ms on SxS switches that were adapted to interpret DTMF.
In some cases with a good pair you could get as low as 20ms but it wasn't reliable.