Three quarters of all corporate telephony lines will be IP-based by 2009, according to research by Radicati Group.
The study found that a majority of companies, especially medium to large sized businesses, are gradually upgrading their PBXs to hybrid solutions.
This allows corporations to migrate to IP telephony at their own pace, rather than completely overhauling their telephony network.
The study focused on vendors of onsite-deployed corporate IP PBXs, both hybrid and pure-play. It did not include hosted solutions or IP Centrex.
Worldwide revenue for hybrid and pure IP PBXs is expected to grow from approximately $1.5bn in 2005 to $9.9bn in 2009.
Meanwhile US research firm Heavy Reading found that 50 per cent of telecoms firm staff worldwide said their voice traffic would be IP by 2007.
The report surveyed 175 carrier professionals representing more than 130 network operators worldwide, including AT&T, BellSouth, BT Group, SBC Communications, and Verizon Communications.
More than three-quarters of the respondents said that their company had already deployed VoIP in some part of its network, and within 12 months that figure will rise to almost 90 per cent.
Over half of respondents said that less than 10 per cent of traffic, in both access and core, is VoIP today, and that the proportion of customers with VoIP-enabled terminals or handsets is even lower.
"The single biggest reason for deploying VoIP is fear that traffic would otherwise migrate to competitors' networks," said Graham Finnie, senior analyst at Heavy Reading.