

How about half a friend?  The Motorola Codex preliminary V.Fast modem
(which you can by right now) does 24.4 kbps (raw) over standard phone
lines.  28.8 kbps is what is usually claimed for the "final" v.fast,
but you can't go out and buy that right now, the standard isn't done yet.

Again, voice can be compressed quite well down to 4000 or 8000 bps
depending on how good you want it to be, but that requires a DSP or a
special ASIC to do in real-time.