How to talk to phones from linux

[John Chambers]

The folks I'm working for have just come up with a  request
that  seems  to  be  difficult to find any real info about.
What they want to do is have their linux boxes (mostly  RH,
various  releases)  initiate  phone  calls,  and send voice
messages.  One example is:

<RING> Hello, Mr.  ___.  Your surgery is scheduled for this
Tuesday at 10:45 am.  If this is a good time for you, press
1; if you'd like to reschedule press 2.

The people involved would really  like  a  completely  open
source  package  to  do this, because they have some fairly
serious security issues (Can you say "HIPPA"?;-)  and  they
need good control over exactly what the software does.  Any
proprietary code would be a last resort.

I've found a cool voice-generating project at  sourceforge,
freetts, and generating the voice from the usual text looks
like it's solved.  (Would you like that in an English or an
Irish accent? Or maybe kevin16 the computer voice?) But how
to get the sound to come out of a remote  telephone  is  so
far  an unsolved problem, as is recognizing when the person
at the other end presses a button.

The only way I've found so far to have  the  computer  send
voice  rather  than  data  is to go through some commercial
services.  We all know that it's possible for computers  to
make phone calls (;-), but the code for doing this seems to
be hidden behind thick layers of secrecy.  Or maybe I  just
haven't guessed the right terms to type to google.

Anyone know anything about this?