For example, Cisco Monday will announce native support for SIP as part of its new Unified Communications system. That capability will enable newer Cisco IP phones to work with third-party applications such as IBM's Lotus Sametime and Microsoft Corp.'s Live Communications Server 2005.

Separately, Citrix Systems Inc. will announce plans to use SIP to integrate its network and application access tools with Cisco's communications software.

And Avaya will introduce a version of its Converged Communications Server that supports a broader range of SIP endpoints, including IP phones from Cisco. Avaya also plans to announce that it's working with about 50 companies, including Citrix, to develop communications applications based on SIP and other standards.

More Cooperation

After years of selling voice-over-IP products that didn't interoperate with one another, vendors are starting to cooperate more closely to bring voice, video and presence-awareness technologies to corporate desktops and handheld devices, analysts said.