Your memory about v.22bis at 2400 bps is entirely correct. v.22 at
1200 bps/baud was the last of the 1 bps = 1 baud dialup modem standards. However, v.32/v.32bis/v.32ter/v.34/v.34bis all use trellis coding and
additional tricks to get high bit rates out of 2400 baud. It is
technically possible to get 2400 bps at 2400 baud from any of these
latter standards, though realistically the only place you'll find
conditions twisted enough to do that is in the lab.
--eric (speaking only on my own authority, as usual)