if i remember correctly the USRobotics only made 33.6 at first but there was a firmware upgrade or so to make V42bis which was 57.6 later .. correct ?
Yes Us Robotics made 33.6 and release v42 bis protocol - another company (winbond i think ) created k56flex... these 2 companies battled it out and so there were technically 2 proprietary protocols for running 56k for the longest time.
aaah yes, yes... this why you had separate phone numbers on some BBS as they had different modem on different lines..