"That transition is extremely young right now," Raab said. Entire networks, including customer-facing infrastructure at the edge, may start to get a wholesale retrofit starting around 2010, he said, though there are many variables that could change that picture over the next five years.

Growth over the next five years will come from a combination of replacing existing infrastructure and overlaying VOIP on current broadband networks in highly developed countries, along with the use of VOIP to reach new phone users in less developed regions, Raab said.

(Stephen Lawson of the IDG News Service contributed to this article)