CQer sends an ICQ invitation over the normal network connection. The invitation is identified by the reciever's CQer program utilizing Caller ID. No real phone connection is used, so sending an ICQ invitation is completely free.
CQer runs in the background, monitoring your phone line for CQers from the people in your CQer list (buddy list). When one is detected, you are notified with visual and audio cues. If it is from someone you have set CQer to repond to, it automatically connects you to your ISP and the ICQ server.
The program can run as a convenient icon in the System Tray area of the Windows taskbar.