When enterprise social and unified communications technologies go walking, which one does the talking? UC, of course, because it has the voice to speak up. So is that where the power lies?

Clearly, social media is very complementary to UC, providing context for voice and video calls by telling you more about the people you're calling or conferencing with. UC is somewhat social anyway because it includes instant messaging, and what is a buddy list but a representation of your social network? What social software adds is the ability to hang profile and contact tags on documents and discussion threads, providing another way of making connections beyond the buddy list and the formal corporate directory.

An enterprise social network also gains from the combination, when users get the option of breaking out of text-based communication on those occasions where a call would shortcut a long chain of messages and let people get their work done faster. On the other hand, I think there is room for debate on how much the convenience of a click-to-call mechanism makes, versus just being able to look up a phone number on a user's profile and dial it.

Public social networks tend to set the direction for what people expect from enterprise social software, and to date they haven't assigned a big role to voice or video. That may change with the advent of hangouts video chat in Google+, which many early users have cited as one of the service's most compelling features.

When I was surveying the competition in enterprise social software at the Enterprise 2.0 conference in Boston in June, I asked many of the vendors about the notion that their niche is really a sub-category within or feature of UC. No one has ever told me that, at least not in so many words, but I suspect that's the way Cisco and some other UC vendors think of it. Certainly, they would like to make the case that you would be better off buying your social and UC from the same party, as part of an all-encompassing technology platform.

Jive Software co-founder and CTO Matt Tucker offered a different theory. "It's remarkable how little progress has been made in unified communications in the last 10 years," said Tucker, speaking as a past board member of the XMPP Standards Organization, which is charged with instant message and presence protocol standards. He sees enterprise social networks being adopted as a much faster pace than UC ever was.

"I think it's more likely that UC gets subsumed into social than the other way around," Tucker said.

I repeated that statement at a Cisco dinner that evening and one UC analyst at my table nearly choked on his scorn, muttering something about that kind of sentiment being "the definition of pure play." In other words, he has Jive pegged as a niche software application competing with more substantial platform technology players.

I got a more politic answer from Mike Rhodin, senior VP of IBM's software solutions group. IBM has both UC and social software products, but Rhodin said he doesn't see UC encompassing the social category. "I think it's adjacent," he said.

"Social is good for one-to-many communications where you don't know the other party," Rhodin said. "In UC, you tend to know the other party." That formulation doesn't entirely make sense to me, given that we typically construct online social networks from friends or followers whom we know to some extent, at least digitally. But certainly there is the element of discovery of friends of friends and social tags attached to documents and blog entries.

That word "adjacent" strikes me as about right, however. Joined at the hip, no. Related and potentially interdependent, yes. And likely to grow together over time.

IT is caught in a squeeze between requests for new applications, services, and device support and demands from upper management to keep budgets lean, staffing light, and operations tight. These are irreconcilable objectives as long as we spend the vast majority of our resources on legacy services. Read our report now. (Free registration required.)

David F. Carr is Editor of The BrainYard, the community for social business on InformationWeek.com, covering social media and the new generation of enterprise collaboration technologies.

Federal agencies must eliminate 800 data centers over the next five years. Find how they plan to do it in the new all-digital issue of InformationWeek Government. Download it now (registration required).