Never used an auto-dialer myself, but it would be trivial to code one. Just send ATDT<number> out the serial port and see if "CONNECT" comes back before timing out.
Back in that time, I think a good rate was $0.01/minute for a local call on a consumer landline. Unlimited calling plans came later. Not attributing any intent to the telco, just saying, there would be no cost issue to motivate an investigation.