However, analysts have questioned whether the technology will take off until standards are finalised and battery issues are resolved.
Chandra Kintala, vice-president for research realisation and network software at Avaya Labs, said, "Handsets and back-end infrastructure for dual-band Wi-Fi and cellphones will be available by early 2004."
The new devices - jointly developed with handset maker Motorola and wireless networking provider Proxim - will potentially allow users to switch from using mobile phone networks outside the office to a wireless Lan inside company buildings or at commercial public hotspots.
The development of dual-band technology will allow businesses to cut costs by allowing calls usually made via mobiles from a building to be routed through the IP network, simplifying the management of employees' calls.
Only one handset will have to be supported, whether employees are in or out of the office.
Gartner analyst Ian Keene identified problems with standards, power and cost as standing in the way of the technology.
"The current generation of wireless chipsets are power-hungry and it will take another couple of iterations to solve these problems," he said.
"There is no voice over IP wireless Lan standard as yet. Also, although some firms will go for the technology, I am not sure they realise the potential cost of being locked into a non-standard product with one supplier."
Analyst Jeremy Green of Ovum said, "Enterprises with secure wireless networks are the obvious candidates to take advantage of this, especially those with lots of mobile workers.
"If employees tend to use mobile phones a lot, the calls will not have to be paid for when they are in the office."