Xerox Corp yesterday added a system that it says can handle more than 3,000 calls per hour and store up to 526 hours of messages to its XVMX Voice Message exchange line: confusingly called the System V, it has 12 to 64 ports and serves 800 to 10,000 users, and Xerox says it is compatible with all major telephone systems and can be either interfaced to or integrated with existing systems; with lower power and cooling requirements, and the smallest footprint, of any system currently available the System V uses a surface mount intelligent port controller, and features a display for system status, and a control microprocessor supporting off-site testing and diagnostics; at $123,000 or $4,700 a month, it is available immediately in the US.