[no subject]

This perhaps a better way to phrase your question and may get you
better answers from people.  Am not sure about this being the correct
news group, though.

So to accomplish what you want to do, I suggest that there would seem
to be two ways to go at it.

One: you start with a telephone that allows a headset to be plugged
in.  The you wire the synth voice output to the microphone wires of
that headset.  There will be likely some impedance issues to look at
and how to control the volume.  And you need to be careful of not
damaging your synth unit.

Your speaker phone system may support plug in additional components
like a second microphone.

Two: place a small speaker wired from the voice syth directly over the
phone's normal voice input (read what one talks into).

Basically you are trying to replace the phone's input signal from the
handset with your synth's out put.  It would be my guess that there
are voice synth devices that have this interface included with them.

 Hope this helps some.  Let us know how this goes.

ClamRake