Cisco Systems has agreed to acquire two small companies that will help it create a common application development interface for its voice, video and data communications platform.

Bringing together technology from privately-held Metreos and Audium, Cisco will develop a common application development interface for Cisco Unified Communications. Cisco agreed to buy the companies in separate deals, both of which require regulatory approvals and are expected to close in Cisco's fourth quarter, ending 29 July.

Unified Communications is Cisco's system for bringing voice, videoconferencing, collaboration and other forms of communication together under a single IP umbrella, along with policies and online presence capabilities. This area is shaping up as a battleground for many vendors, where what Cisco wants to do may rub up against the plans of Microsoft as well as of other networking companies.

Metreos' technology will help Cisco system integrators, resellers and other partners build applications for the Unified Communications System. Cisco said that Audium would help enterprises build automated voice response systems. The two would be integrated over time, to form one application development interface for Unified Communications, said the company.

Cisco agreed to pay about $28 million in cash for Metreos, a five-year-old company in Austin with 19 employees. It will pay $19.8 million in cash for Audium, which was founded in 1999 and has 26 employees based in New York. After the acquisitions close, the companies' workforces will be brought in to Cisco's Voice Technology Group.