And why are you limiting this to V.32 (9600bps)? V.32bis (14.4k bps) modem chips cost maybe 20% more than v.32 chips in quantity.
Even higher speeds are available if you're willing to go that far. Zyxel v.32bis modems have proprietary 16.8 kbps and 19.2 kbps full duplex raw modulation rates, but they use DSPs instead of modem chips like the ones from Rockwell, AT&T, and Intel. I believe there are some v.FAST (not CCITT compliant) modems like the one's from Motorola (Codex) that can do 21.6 kbps and 24.0 kbps. I believe the final speed of v.FAST once standardized by the CCITT will be 28.8 kbps.
I don't see how a 28.8kbps (raw) data rate is possible, as the Shannon limit for a POTS line is 22kbps. Certainly parts of the phone system no longer impose the narrow bandwidth that are part of the 'spec', but one can not always depend on getting a line that exceedes the published parameters of the phone system. The Rockwell (RC96AC/RC96ACL/RC144AC/RC144ACL) modem chip (set) has an on-board codec that does ADPCM in hardware. It makes for a very nice programable answering machine. Interestingly, the designers guide has someting to say about bit rates. At a sampling rate of 7.2 KHz, (the only sample rate this chipset supports) 8 bit samples are presented at a bit rate of 57600 bps. Add in a start/stop bit, and you now need a DTE rate of 72,000 bps. Most UARTS don't support this rate, and thus you will need to find one that will run at 115.2 Kbps. Drop to 4 bit samples, and you get a bit rate of 28,800 bps, for a required async DTE speed of 36,000. (or 38400 bps on most uarts.) I'm also fairly sure that recent Zyxel modems (e.g. the U-1496) use this Rockwell chip(set), and not a dedicated DSP. Jim