Microsoft chairman Bill Gates stood before a crowd in San Francisco on Tuesday to announce the release of Microsoft's unified communications products, proclaiming the beginning of a shift that would be "as profound as the shift from typewriters to word processing power," with Microsoft leading the charge. The truth is a bit messier.

There's no doubt Microsoft and its Office Communications Server (OCS) are playing from a strong position. Unified communications, which combines voice, video, messaging, and collaboration into one computer-based platform, brings the once-hardware-dominated world of communications into the software age. Microsoft once did that for office productivity tools, hence Gates' reference.

It promises to eventually replace that many-buttoned phone on your desk with a piece of software and the cobweb-draped PBX in the closet with some software and an off-the-shelf server from Hewlett-Packard or Dell. Microsoft arguably did something analogous to the computer itself. Yet but for the marketing blitz, the road is long and windy.

Microsoft isn't even telling customers to get rid of the old stuff yet. "We're definitely not advocating a rip-and-replace type solution," says Kim Akers, Microsoft's general manager of unified communications marketing. Instead, Microsoft is advocating customers keep their old telephony infrastructure up and running if they want, initially applying OCS to underserved niches like teleworkers. Microsoft reports that there were about 300,000 deployed seats -- a staggering number for such an emerging technology -- during testing phases, but it's not clear just how much or for what they were used.

The biggest challenges for Microsoft may be those pesky legacy vendors, Cisco Systems, Avaya, Siemens, et al. Those guys are known for resilience and uptime, a critical feature for phone calls, and it's gained them a big toe-hold in the quickly growing world of VoIP. Microsoft's admittedly not known for superb uptime in comparison. Computers crash, phones rarely do. "Voice is the one place where the [reliability] question comes up," Akers says. "They say, 'Hey, you're a new entrant into voice. Prove to me that you're going to be reliable.' "

She proceeds to rattle off a few proof points: Microsoft has adaptive voice codecs that analyze network traffic and adapt in real time to maintain voice quality, research firm Psyteknics compared Microsoft voice quality with others and found Microsoft at or above the competition, and Microsoft's Quality of Experience Monitoring Server that's included with OCS gives IT pros a view of the network and a look into sound quality.

Still, it might take Microsoft a few years to gain the chops. Microsoft's partnership with Nortel on OCS shows Microsoft knows it needs some and has some expertise to gain from the network companies. And it could take some shift in the way the public thinks, too. For example, most of the phones being announced Tuesday and before plug into the PC via a USB port, rather than directly into a wall Ethernet jack.

All that could give the other guys a head start if Microsoft isn't slick enough. "There's six or seven years of pure carrier development and then another three to four years of enterprise and carrier development on top of our solutions. We think by the time they're really ready to deliver enterprise communications, we'll have hundreds of thousands to millions of users installed," says Siemens senior VP Mark Straton. "To be honest with you, we thank Microsoft for helping us get this message out there in the market."

Interoperability's another hurdle. Though Cisco's and Microsoft's CEOs got on stage in August to appear buddy-buddy about unified communications, they're not going to work together unless forced by their customers, says Forrester Research analyst Henry Dewing. The SIP standard, which, for example, lets any number of standardized phones make calls on any SIP-compliant VoIP system, is still gaining features and isn't yet as rich as many business phone systems are, overall. Microsoft's trying to tackle this, at least partially, by publishing OCS interoperability specs and creating a "certification program" to get competitors to make their systems compatible and make them able to federate.

"Ten years from now, when people think about telephony, they'll see a movie and look at a desktop phone and think, oh yeah, we used to have one of these," Gates said in his speech Tuesday. A decade's a long time.