Microsoft is acquiring a Swiss software company that specialises in VoIP (voice over IP) applications with a view to adding such a function to its Office products, it announced on Thursday.

The world's largest software maker will acquire AG, a Zurich-based company, for an undisclosed amount. The technology it gains as a result of the deal will help it add VoIP to the Office Live platform, which already supports real-time communications via channels such as instant messaging.

VoIP is a hot area of the IT industry at present, as demonstrated by eBay's $2.6bn (£1.46bn) acquisition of Skype Technologies SA last month. Its image has been changing from something that consumers use to make cheap, low-quality voice calls via their PCs, to a more stable technology suitable for professional applications such as business.

Microsoft took some big steps into the VoIP space in March this year when it launched a new IM client, Office Communicator 2005, and added enhancements to its Live Communications Server 2005 and Live Meeting Web conferencing service.

"VoIP is exploding," Bill Gates, Microsoft's chairman and chief software architect, said at the San Francisco event. "We want to enable the software richness on the PC to connect out to traditional PBXs."

The company followed the March show with a string of deals. In June it formed tie-ups with AT&T, Amdocs and Sylantro Systems to work on various VoIP systems, then in August it acquired Teleo, a developer of services and technology that allow users to make and receive voice phone calls on their PCs via the internet. A month later Microsoft said it planned to work with Qwest Communications International to provide VoIP services to small and medium-sized businesses.

As a result of the latest deal, will become part of Microsoft's real-time collaboration business group, which is led by the software giant's corporate vice-president, Anoop Gupta.

Microsoft will continue to offer's software on a standalone basis and existing customers should see no immediate impact from the acquisition, the management of the Swiss company said in a letter to customers, a copy of which was posted on its website.