"IP telephony has gone mainstream," says VoIP analyst Brian Riggs, of Current Analysis. "There's no doubt about it."

Planned and ongoing VoIP rollouts at Bank of America, The New York Times Co., Amazon.com, Chicago public schools, University of Pittsburgh Medical Center and dozens of other enterprises all point to the acceptance of VoIP as the new standard for business telephone and messaging systems, analysts and users say.

Not that telecom professionals are entirely abandoning more than 50 years of digital PBX technology. Many are mixing IP and time division multiplexing TDM technologies for now as they wean employees off of the old phone equipment.

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The shift in market dominance from TDM to IP really became apparent in the first quarter of 2006, according to research firm Synergy Research Group. Two years ago, only a third of business phone system lines were IP, but by this year's third quarter, more than 60% were. (Enterprises have spent $7.7 billion on telephony in the first three quarters of 2006, according to Synergy).

So what has prompted the shift?

"What changed over the past few years is that nothing changed," Riggs says. Products from companies such as 3com, Avaya, Cisco and Nortel have matured, not undergoing the disruptive changes seen in the early 2000s. Many of the questions regarding feature sets, stability and quality have been addressed, he adds.

IP telephony products and standards are at the point where some organizations are even comfortable with open source technology.

Amazon.com announced earlier this year that it is deploying the Pingtel SIPxchange Enterprise Communications System, an open source IP PBX, based on Linux servers and SIP phones, to support thousands of users at its Seattle headquarters. Separately, Sam Houston State University in Texas and the Southern Co. are going live with the open source Asterisk VoIP platform, in enterprisewide rollouts and in small-pocket deployments.

"We have a lot more peace of mind with the open source system," says Aaron Daniel, senior voice analyst, Sam Houston State University.

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