🚀 go-pugleaf

There are lots of chips out that will decode touchtones; my favorite
is the SSI 202 chip, available at RatShack for only twice what it is
at chip stores.  It will give you 4 bits of data telling you which
button is pushed, plus a DigitValid output.  This is easy to read
on a parallel port.

For simple voice response, use one of the many voice synthesizer
chipsets that are on the market.  My favorite for simple stuff is the
DigiTalker, again available at RatShack.

You need some sort of coupling circuit to connect these to the phone
line.  Ignoring for a moment all the FCC part 68 interconnection
licensing requirements (oh shut up, all you Pharisees!), all you
probably need is some sort of isolation transformer and a little
amplification for the synthesizer.  Cannibalize an old 300-baud modem
for this, and you'll probably get a free ring detector circuit in the
bargain.
	- Brian