IBM Enhanced Audio Conferencing (IEAC) is a VoIPbased audio conferencing system that, like several other systems, provides a visualization showing who is present and their states (e.g., speaking, muted). This paper presents the first study of the use of such a system. Drawing on log files collected over six weeks of use by over 1300 corporate employees, and interviews with 10 of them, we look at how and why various features of the system are used and what sorts of practices are supported. Our findings shed light on the factors that drive the use of visual enhancements to audio conferencing, and suggest further research topics. Author Keywords Audio conferencing, conference call, social translucence, social proxy, social visualization, telephony, VoIP, voice ACM Classification Keywords H5.2 [Information interfaces and presentation]: User Interfaces. - Graphical user interfaces.