...

...

For modem to modem communications, start and stop bits were used up through 2400 baud when one bit = one tone. The method of one bit = one tone was dropped for other forms of encoding when modems started supporting connection speeds in excess of 2400 baud.

I assume you mean 2400 bps modems, i.e., v.22bis? Admittedly, it's been a while since I used one, but my recollection is that 2400 bps modems operate at 600 baud, with 4 bits/baud using QAM.

This matches my recollection. I think it was 1200 bps that was the last 1 bit per baud modem.

Cheers, -- jra

Yes and no. The Bell 202 was 1200 bps, one bit per baud, half duplex on a switched line. The Bell 212 was 1200 bps, 600 baud, 2 bits per baud, full duplex. So was the Vadic 3400, which preceded the 212.