Plans to deploy VoIP are soaring, but enterprises still have a hard time justifying costs to upper management.

According to a survey by BT INS, 62% of respondents either have deployed or are in the process of deploying VoIP across their networks -- up from 44% in 2005. Another 18% are designing or testing VoIP deployments for limited network segments.

At the same time, however, cost is becoming a more significant barrier to adopting VoIP, the survey found.

In 2005, justifying costs to upper management ranked fifth among a list of 15 possible barriers to adoption. This year, that worry rose to the top of the list, with 46% saying it was a significant barrier.

Cost justification shared the top spot with technical integration issues, which also was cited by 46% of respondents as a significant barrier. The cost of network upgrades to support QoS ranked third among the adoption barriers, cited by 41%. Concern over lack of standards dropped slightly; just 28% listed it as a concern this year.

The survey also reflects a shift in how customers plan to deploy VoIP. In 2005, 57% said they would gradually replace traditional telephony gear with VoIP gear. That number has shrunk to 39%. Now 45% say they will either replace their traditional PBX with an IP PBX or other VoIP products.

BT INS asked respondents to rank a list of criteria for choosing VoIP on a scale from “not at all important” to “very important.” The top five criteria, in order, are: network reliability, voice quality, security, network manageability and service guarantees. All five were criteria very important in 2005 as well, with voice quality gaining even more importance in 2007.

Meanwhile, the biggest hurdle to overcome in replacing traditional phone services with a VoIP service is demonstrating cost savings; 32% of respondents cited that problem. Roughly 22% said the possibility of lower voice quality in combination with network availability was the biggest hurdle to overcome.

BT INS conducted its survey between Feb. 22 and March 31 with 157 IT professionals who signed up to receive information about the IT software consulting firm. Respondents classified their organizations by numbers of employees they support. Of those who answered, 28% have less than 100 employees, 20% have 100 to 999 employees, 19% have 1,000 to 9,999 employees, and 33% have 10,000 employees or more.