If the person on the telephone side of the call is hearing echo it is usually caused by the sound card or the speaker and microphone arrangement. 

If you are using an open microphone and speakers, try turning the volume down and make sure the microphone is closer to the person speaking than the speakers.  We recommend using a headset or handset.

You can adjust your CrystalVoice settings, in CrystalVoice LIVE click Options.  In the Options window, choose the Audio tab.  On the Audio tab, choose Mic and Speakers (even if you use a headset) and click OK.

You can also mute the playback of your microphone through your speakers - this will not mute your microphone to the person you are calling.  Go to Start->Programs->Accessories->Entertainment->Volume Control.  In the Volume Control, click the Mute box under the Microphone control.