 and ven- dors did not enter the IP game enthusiastically. Early entrants arrived Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Telephony Telephony with enhancements to existing equipment that were proprietary and expensive and did very little to raise customer awareness or engender trust in the vendor's migration strategy. Over time, however, PBX man- ufacturers began to embrace the concept of convergence as their cus- tomers' demands for IP-based systems grew, and, soon, products began to appear. Most have heard the message delivered by the customer: Pre- serve the embedded base to the degree possible as a way of saving the existing investment; create a migration strategy that is seamless and as transparent as possible; and preserve the features and functions that customers are already familiar with to minimize churn. Major vendors like Lucent Technologies and Nortel Networks have responded with products that do exactly that. They allow voice calls and faxes to be carried over LAN, WANs, the Internet, and corporate intranets and function as both a gateway and gatekeeper, providing circuit-to-packet conversion, security, and access to a wide variety of applications; these include enhanced call features such as multiple line appearances, hunt groups, multiparty conferencing, call forward, hold, call transfer, and speed dial. They also provide access to voice mail, CTI applications, wireless interfaces, and call center features. An Important Aside: Billing as a Critical Service One area that is often overlooked when companies look to improve the quality of the services they provide to their customers is billing. And while it is not typically viewed as a strategic competitive advantage, studies have shown that customers view it as one of the top considera- tions when assessing capability in a service provider. Billing offers the potential to