The wireless VoIP application is part of its Microsoft’s Office Communicator Mobile offering, which is a unified bundle of instant messaging and presence that connects to Microsoft’s popular Outlook e-mail server. The package is slated for release in about two months or so and will be a free add-on to Microsoft Office Live Communications Server 2005.

The VoIP component of the bundle seems to have largely been lost in the shuffle of press announcements at last week’s 3GSM conference in Spain. And Microsoft itself said the service is not the focus of the mobile version of its Office Communicator.

But for the VoIP and unified messaging industry, it shows that Microsoft is flexing some serious muscle in the coveted mobile enterprise market.

It’s a recognition that they need to strengthen their value proposition, because the enterprise market is going to be more competitive for Microsoft as the alternatives are becoming real, said Jon Arnold, principal of VoIP analyst firm J. Arnold & Associates.

The Outlook database is really the care DNA of everything that’s going on in the enterprise . . . but the key for Microsoft is that they’re not cut out of the loop.

At first, Microsoft’s VoIP service will work only on WiFi-enabled Windows Mobile 5-based devices. Paul Duffy, senior product manager of Microsoft’s Unified Communications Group, said the company was working with other mobile device makers to write clients so the Office VoIP service can also run on alternative operating systems. Duffy declined to provide details of those partners.

The mobile VoIP service would enable, for instance, free VoIP calls between workers’ mobile phones throughout an enterprise campus over a secure company WiFi network.

Duffy said the VoIP capability was added because more people are using mobile devices inside the enterprise and more devices are adopting WiFi networks. Moreover, Microsoft is attempting to follow the trends of workers with its unified communications applications. Mobile was the logical next step and something that customers are asking for, he said.

Mobile is not just about VoIP-over-wireless networks. The main focus of what we’re bringing here is secure instant messaging and presence, and integrating it with VoIP, Duffy said.

Of course, Microsoft is not alone in its mobile unified communications strategy. As VoIP makes its way into the mainstream business market, different applications and communication modes converge.

There’s the convergence of wireless and wireline communications, traditional PSTN telephony and IP communications, and of different wireless technologies that are starting to gain acceptance into the marketplace, such as WiFi, WiMax and 3G Arnold said.

On top of that there’s another convergence that’s happening of voice-enabled end points, that is, devices that will work with IP, he said. It means more ways for people to bring mobility into the enterprise. Microsoft feels the need to be in the picture.

And with the most prolific enterprise e-mail application in Outlook, Microsoft has a good starting space.

But Microsoft’s foray into the mobile VoIP space won’t squash the rest of the industry, Arnold said. The wireless play of others, notably Google Inc and open-source applications such as Linux, will be a force to be reckoned with.

Google, for example, has integrated its mobile search capabilities with VoIP, as well as e-mail and instant messaging, Arnold noted. This is a potential threat to Microsoft, he said. It doesn’t take long for these shifts to happen . . . the rise of these Web-based alternatives is a threat to Microsoft’s software business.

The rise of open-source also looms. There are open-source models out there that do pose a threat to Microsoft in the enterprise, including Linux, Arnold said. Open source has a ways to go, but what’s emerging now are alternatives to the Microsoft money machine.

And while Skype Technologies SA may not yet be a force in the enterprise, the company clearly is also focusing on mobility and has already made some WiFi announcements. Skype might also emerge as a mobile unified messaging rival to Microsoft in enterprise market, Arnold said.

Google, Linux, Skype and lesser-known companies, such as the business-focused VoIP company Popular Telephony, are all becoming more and more real as alternatives to Microsoft, Arnold said.

After all, vendors know the consumer VoIP market is quickly becoming a commodity and a race to zero, Arnold said. The enterprise market has more resources, more revenue opportunity for these vendors to bring VoIP applications to market.