Up to now, people making their internet phone calls from a PC have used a microphone and speaker connected to the soundcard. Others use a headset combining earphones and a microphone.

Both of these systems have their drawbacks:
The use of a speaker limits the privacy of the phone call and gives the familiar feedback problem when the microphone picks up the speaker output.
The headset solution avoids the feed-back but does not allow you to hear the ring of an incoming call, unless you keep it on your head all the time...