I recently posted: Use my PC as an Extension Phone. I have given this alot of thought and realize that the problem is about whether there are any modems that will accept voice input from the pc microphone. My V90 modem does play phone sounds including voice overr the pc speakers but will not recognize my microphone. If anyone knows if there's software that will accomplish this or any related websites please let me know.
Make sure that your sound card is set up properly to use a microphone. Most sound cards these days use the mic jack as a speaker jack. Find your sound card manufacturer and check the layout of the jacks.