The Great Idea Finder was quoted on the History of Hayes Modem on Date: Sun, 8 Jan 2006 20:56:30 -0600:
Fascinating facts about the invention of the PC Modem by Dennis Hayes in 1977
The earliest Hayes modems were knock-offs on the Bell Standard 103 modems, 300 baud full duplex. Hayes did innovate the escape sequence (+++) and the command set (the AT commands).
Similarly, the 1200 Baud Hayes modem was a knock off of the Bell 212 standard modem, adding the escape sequence and the command set.
I believe that the early 2400 bps modems may have involved a Hayes standard protocol. But from 9600 bps, the standards all came from industry bodies, such as the ITU. "Baud" is correct for the slowest modems, but "Baud" actually refers to changes of state. The 2400 bit per second modems were 4 bits per baud IIRC, and all later modems send multiple bits per baud
Direct replies are unlikely to be read. To reply use the address below: falco(underscore)md(atsign)yahoo(dot)co(dot)uk