Take a look at AMD's 'world modem' chip.  I cannot remember
the number off the top of my head, but these are used in alot
of TNC's in the amateur radio world.  I believe its limit is
possibly 1200 baud though.  Also look at EXAR.  Should be able
to get any 2400 baud part for cheap, but be carefull that you
don't design something in that is for production, as many of
these either will become obsolete as soon as the board is done
or just can't buy 'em anymore (anyone got a few thousand 64K
static rams in a zip package ?).  If you just need a few for
your home project, should be able to get several different
flavors sampled.  Good luck.