Skype lets you make free PC-to-PC calls with your microphone and some other features, but I'm not sure if that's what you mean. http://www.skype.com i think
I use a program called "InternetCalls", lets me make free calls to a lot of landlines around the world using my headset. I'm not sure if this is what your after, but I thought I'd put my two cents in. http://www.internetcalls.com/
I use a program called "InternetCalls", lets me make free calls to a lot of landlines around the world using my headset. I'm not sure if this is what your after, but I thought I'd put my two cents in. http://www.internetcalls.com/