Does to second counter on the phone start incrementing? Does it look like the call is connected? If so, you should check on the Unity status monitor web page to make sure the call it connected and that the correct greeting is being played.
If you are getting that far then it is probably a one-way audio issue. i.e. the packets that Unity is sending are not going to the correct IP address or they don't have a route to the phone. Make sure that Unity does not have two NICs or two IP addresses. After that make sure Unity can ping the phone.
If you are not getting that far let us know.
Keith