SAN FRANCISCO - In contrast to the media frenzy surrounding the debut of video game Halo 3, Microsoft ( MSFT) has been quietly bringing out the bits and pieces of a system that ultimately will mean far more to the software giant's top line.Although Halo 3 earned $300 million in its first week, sales are expected to taper off after the holidays. Unified communications, however, is already a $1 billion business and will be a growth engine for years to come, Business Division President Jeff Raikes said Tuesday at the system's formal launch. With the delivery of Office Communications Server 2007 and Office Communicator 2007 this month, the system relies on familiar business software packages, such as Exchange Server and Live Meeting, and a few hardware bells and whistles. The Microsoft platform is designed to transform the way employees work with each other. Predicting it will someday replace the single-vendor PBX phone system, which typically has no ability to communicate with corporate computer networks, Chairman Bill Gates said Microsoft has incorporated into office networks the last remaining island: the phone. Both corporate and mobile phones can finally connect easily with computers and VoIP networks. "The transformation to software communications is going to be as profound as the shift from typewriters to word-processing software," Gates said. The system gives users a single user-interface with voice recognition to manage all phone, email and web conferencing, Raikes said. A key feature is its ability to show the status of employees, what Microsoft calls "presence," no matter where they are. Online employees can be listed as available, busy or engaged in a web conference, and their managers can pull them into a conference with a drag-and-drop click.