"People still use their regular phones. But we are encouraging them go to OCS for all internal calls," Kaldestad said.
The voice quality through OCS is pretty good, Kaldestad said, and better than the regular phone network between many of its international offices.
Lionbridge did not roll out any additional networking gear to support VOIP, though it did set its routers to prioritize VOIP traffic. That was only needed for employees in offices with heavy Internet use, said Kaldestad.
2) Can I really expect some Microsoft software running on a Windows box to be as reliable as a PBX?
With OCS, users can centralize what were formerly hundreds of scattered PBX boxes onto just one or two servers. That can simplify management and make it easier to fix things when problems arise. The flip side is that if a problem with the OCS software occurs, the chances of a "catastrophic failure" bringing down all of the phones companywide is much higher than with an individual PBX.
"If you're all IP and SIP trunking and you lose connection to your carrier, that's not a very good scenario," NEC's Lopez said.
Analysts such as Barry Marks at IntelliCom Analytics agree.
"Vendors such as Avaya, Nortel and Ericsson all understand customer requirements for reliability, availability and hardened environments," he said. "Some of the newcomers who haven't been down that road could be at a little bit of a disadvantage in terms of truly ensuring 'five 9s' of reliability."
The other aspect is that OCS runs only on Windows Server 2003 and, soon, Windows Server 2008, unlike most competing products, which run on Linux or proprietary "hardened" operating systems.
Windows' lack of reliability "is totally out there as a perception and a message," acknowledged Kim Akers, Microsoft's general manager for unified communications. But she pointed out that other unified communication products, most notably Cisco's CallManager, also run on Windows Server.
Dustin Hannifin, a systems engineer at accounting firm Crowe, Chizek and Co. who has been beta-testing OCS, argues that OCS -- if architected properly -- may prove safer than conventional PBXes.
"The problem I have with traditional PBX systems is that while they are generally rock-solid, when they fail, there is no redundancy plan," he said. "For instance, with the old Octel [voice-mail] systems, there is only one hard drive. At least with OCS, you can back things up."
That's what Microsoft recommends: Users should replicate their main OCS server continuously to a redundant server in a different physical location.
For now, that isn't necessary for Lionbridge, which has had 99.88 percent scheduled uptime in the last nine months, Kaldestad said.
The firm runs two load-balanced OCS servers out of the same data center. That allows the company to keep one server running while it patches or reboots the other. And if both servers were to fail at the same time, Kaldestad is confident he could bring up a replacement OCS server in several hours because "all of the really important configuration data for OCS is stored in Active Directory."
Finally, Microsoft strove to make OCS interoperable with PBX and IP PBX gear from a number of vendors, so that customers can hold onto their boxes as long as they want.
"If you're the type of company with lots of mobile workers and consultants who demand a lot of features, you might go 100 percent software right away," Akers said. "But most customers will move in stages and wait for the natural end of life of their PBXes."