It's possible to make a false preliminary pulse with any analog
> phone, not just candlesticks. A false preliminary pulse equates to
> dialing a 1 no matter what kind of equipment is at the other end,
> even ESS. As we've discussed on this list any number of times
> before, an experienced high school kid can dial any number by
> punching the switchhook button.
According to the Bell System history, the problem was unique to candlestick phones. Why only those phones, I don't know. I'll have to read up on it to get more details.