orse the accuracy, the lower the value. Productivity enhance- ment depends on accurate presence data, and accuracy is achieved by combining multiple sources of presence data. There are many sources for presence data within an enterprise, such as detecting whether somebody is on a call or off a call, based on information from enterprise phones; determining whether a person is in a meeting or out of a meeting, based on information from the enterprise calendar systems; deter- mining whether a person is in a conference or out of a conference, based on enter- prise conferencing systems; or determining whether a person has logged in or logged out of the enterprise IM system. Enterprise presence applications show presence on IP PBX phones and on PC- based IM applications. They can also support presence-based call routing as well as Chapter 9 IP Services voicemail ringback. Two standards are involved in presence. The SIMPLE standard is a set of SIP extensions for IM and presence supported by Microsoft, IBM, Sun, and Novell. A competing standard, Extensible Messaging and Presence Protocol (XMPP), is an XML-based extensible open-source option that drives the Jabber IM client (www.jabber.com). For all the good news about presence, there are also arguments against it. Most revolve around IM and the perception that it is intrusive and, at times, invasive. Most companies today use some form of IM, through mostly public services. The industry forecasts that we are only one to three years away from embedding pres- ence in enterprise applications. Of course, standards, privacy, and security are major concerns. SIP is creating new opportunities for platform providers that are introducing new soft phones. Proprietary soft phones incorporate SIP-based presence capabili- ties across both voice and IM, secure SIP-based IM behind the corporate firewall, IM archiving, click-to-talk voice functionality, speech-to-text functionality, and specialty modes for road warriors and telecommuters. There are also open-source SIP products. Not only