I never tinkered with changing the pulse rate, but
> there were AT commands to do that as well. I think in foreign
> countries the "make/break" ratio of pulses was different and I didn't
> want to risk screwing up my modem/software with an oddball setting.
Yep. Here in England it was common to have an AT&P1 command in the initialization string to set the modem to a 67/33 ratio. In practice, the default U.S. setting almost always worked perfectly anyway. I don't recall ever having problems on the default setting when dialing out from the small SxS office which served my area in the early 1980s.
The make/break ratio would probably become a problem only if tolerances on a particular switch were right on the limits.
- Paul.