Chapter 8 referring to the revenue-rich nature of these services. They cost compar- atively little to deliver, yet offer good revenue returns. That's why service providers count on them. So if data is the killer application for voice networks, what's the killer application for data networks? The entire industry is scrambling to build IP networks, to add broadband access in any of a variety of forms, yet every economic study ever done shows that the revenue generated by the data transported over service provider networks accounts for a small fraction of their actual revenue-as little as 5 percent according to some studies. The answer, not surprisingly, is voice-in addition to a growing array of potentially lucrative data-dependent applications. What is inter- esting, however, is that as we stated earlier, the marketplace is not look- ing for the next great killer application-what they are looking for is a killer new way to access existing, utilitarian applications such as voice, e-mail, instant messaging/short messaging, Web access, content delivery, security (hence the success of wireless VPNs), caching, and storage. Fur- thermore, instant messaging is not an application targeted exclusively at teens and preteens: Industry reports indicate that nearly 100 million enterprise employees rely on some form of IM for intracorporate com- munications, and many corporations have seen a measurable decline in e-mail volume as a result of growing IM usage. The phenomenon is decid- edly human: Most employees, upon receipt of an e-mail message, decide whether they must respond immediately or can delay the response until later. IM users, on the other hand, psychologically feel an obligation to respond immediately to the appearance of an instant message-as if the sender knows they are in their cubicle. The result of this is that infor- mation flows more quickly, resulting in an acceleration of decision mak- ing. There is a downside, however: IM users are scattered across a handful of providers including AOL, Microsoft, and Yahoo