Telephony Modem and Sound problems

Hi, I have Dell Dimension 24000 with a Conexant D850 56K V.9x DFVc
Modem. Now I have recently found the Phone Dialer Program buried in my
copmuter. I decided to give the phone thing a try. I plugged in my
Phone Land Line into the phone port into the back of the modem. I get a
connection and can call to other phones using the dialer. However, I
can get no sound from either end but when pushing a number on the
number pad on my computer the other phone gets the tone. I can't hear
my voice on the other phone and I can't hear what the person on the
other phone is saying. I have read other things about using a cable to
connect a modem to the sound card adn tried looking inside my copmuter
but found no obvious connectors for a cable. I have tried other
applications and other phone dialer programs, but still no sound. I am
wondering if it might be my sound settings or something besides the
modem but I am not sure. Please help me if you had the same problem or
any ideas how to fix this. If you know of a better subject group to put
this in please let me know, this is my best guess for a group.

Thanks