As part of what is shaping up to be another hotly contested land-rush between the two, Microsoft and IBM used last week's VoiceCon conference to mark their territory in a race to provide unified communications technology to corporate users.
The focal point was IP-based voice and the infrastructure that will drive it.
Experts say the two companies, as well as the likes of Nortel and Avaya, clearly see software as the future with the PBX and IP PBX playing a niche role.
"I think this is shaping up to be very similar to the e-mail battle," says Rob Koplowitz, an analyst with Forrester Research. "That has been pretty epic in my mind; the way these two vendors have come after each other."
Some see a more complex battle that involves more companies, such as traditional networking vendors Cisco, Nortel and Avaya, and more moving parts, including business process and other applications, instant messaging, presence, video, data, voice mail and conferencing.
At VoiceCon, Microsoft said it would ship the first public beta of Office Communications Server 2007 and its Office Communicator 2007 client, giving customers the first glimpse of Microsoft's future VoIP platform. The company also trotted out customer Royal Dutch Shell , which said it will roll the Microsoft software into production beginning next year and indicated that software was the future of IP voice.
"Ultimately, we don't see the need for separate IP telephony and Microsoft messaging platforms. That is our vision, but it depends on whether Microsoft delivers," said Johan Krebbers, group IT architect at Royal Dutch Shell, during his VoiceCon presentation.
And Krebbers hinted at the obstacles telephony providers face as their industry morphs. "Most [Internet telephony] providers don't understand the desktop very well. Most providers come at it saying 'We're the center [of the network].' "
For its part, IBM unveiled a partnership with Cisco outlining integration of the Lotus Sametime client with Cisco IP phones, voice mail and conferencing technology. The pair also plans to create a standardized client that incorporates APIs from both vendors and gives developers a framework from which to build applications that incorporate unified communications.
The announcements, observers contend, highlight that IBM and Microsoft are going to be the future dominant gatekeepers of voice infrastructure.
"If you look at IBM's announcements, they reinforce that the next [voice] platform is a software abstraction, that more things will move up to the software layer, that they are not going to be hardware, that the network will have a role, but you don't want to put too much into the network," says Mike Gotta, an analyst with the Burton Group. "The roads that I see lead through Microsoft and IBM."
Gotta says the difference between the two vendors is how they get there.
"You have IBM looking at its portfolio and asking, 'Where am I strong -- Eclipse-based clients, Sametime, our developer model -- and where am I weak -- our back end is not coherent, we really don't do audio and video,' " says Gotta. "They draw a line in the sand and say communications vendors come play with us."