you can use Flash and Flash Media server (aka Flash Communication server) to do live audio two way conferencing. The Flash player can receive audio input from the web page user's microphone (user's computer must have a microphone) and send it out to the server which relays the audio stream to a Flash app in your office.

however, you must have access to Flash Media Server and develop the web page app, the server side application to manage the 2 way stream and the app in your office, which may be very similar to the web page app.