Enterprise adoption of voice-over-IP services is growing, but at a pace much slower than expected.

Australian companies trialling the technology warn that large-scale deployments are complex and costly, but there are some local success stories.

One IT manager at a manufacturing company said at first look, VoIP solutions look like a money-saver but when "you consider the upgrade to the networks and then the additional resources need to support it, the total cost of ownership looks a bit different".

But there are advantages in some cases and there have been a number of successful upgrades in recent months at local councils and universities.

National Foods IT security manager Andreas Tilch said the benefits are obvious at times when managers from Sydney are in the Melbourne office for a few days.

"By using the IP functionality of the PABX we can redirect their phone to their desk; by only supporting a handful of users at a time, it is much easier than on a larger scale," he said.

Following a trial last year Logan City Council in Brisbane decided to better utilise the fibre links in its data network and install VoIP in its four main remote depots.

The council serves 170,000 people living across 250 square kilometres and IS services manager Jim Barclay said its legacy phone systems couldn't meet call demands at remote sites, which eroded customer service.

"Where a small number of tie-lines connected the remote system, a blocking situation would occur and residents couldn't get through because all the lines were busy," Barclay said.

The council assessed two options, a number of small PABXs for the remote depots for significant capital outlay, or upgrade.

The Nortel Networks Meridian PBX was IP-enabled through the addition of an Internet Telephony Gateway (ITG) card.

While 80 per cent of the council's 700 handsets are connected directly to the Meridian, the remaining handsets at remote depots are systematically migrating to VoIP.

"As we had already invested heavily in fibre and switching technology for data services to the remote depots during the upgrade, it was logical to make best use of these improvements to reduce our voice-related costs," Barclay said.

"It has streamlined call management and made it easier for staff; other departments still using key systems have seen the benefits of the feature transparency of the VoIP handsets, like being able to access voicemail from anywhere in the depot and now they want to make the change.

"The use of VoIP technology to leverage an investment in a data network should be very attractive to other organisations like ours, where an existing PABX can be upgraded with an ITG card, to deliver all the network features to remote sites via IP."