But not all VOIP applications are created equal. A report from Allied Business Intelligence Inc. (ABI) says the future of VOIP is in hosted or advanced applications, in which carriers offer to outsource VOIP for enterprise customers.

One is the technique called IP Centrex or hosted IP-PBX. This is an IP-based version of the traditional circuit-based Centrex option, whereby a company's internal functions are hosted by the phone company. Centrex is widely seen as a way to outsource functions that otherwise would require an in-house PBX, supervised by internal staffers. On the downside, the approach forces businesses to rely on their carriers for new features and upgrades.
According to ABI, hosted IP-PBX accounted for about $16 million in worldwide VOIP service revenues in 2001, roughly 35 percent of total sales. By 2008, hosted IP-PBX revenues will have grown 39 percent to over $9 billion and will represent more than 25 percent of worldwide VOIP service revenues.
Interestingly, another research firm, IDC, predicts similarly high growth for hosted IP Centrex (up to $6.7 billion by 2007 -- see IDC Predicts VOIP Battle). But IDC says carriers must act quickly to get the benefit of this market, as equipment vendors such as Alcatel SA (NYSE: ALA; Paris: CGEP:PA), Cisco Systems Inc. (Nasdaq: CSCO), Nortel Networks Corp. (NYSE/Toronto: NT), and Siemens AG (NYSE: SI; Frankfurt: SIE) will be aiming to woo away customers with enterprise-based solutions.
ABI says another area of promise in hosted VOIP is the call center, through which a carrier provides the technology for companies to use in customer-service departments that rely on phone input. IP-based videoconferencing is also key to the future of hosted VOIP.
— Mary Jander, Senior Editor, Light Reading