See M$ KB: How to use the GAL Modify tool

Works super too.

Quote:

INTRODUCTION
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You can use the GAL Modify tool to modify personal information that is displayed in the global address list. The GAL Modify tool is located in the Tools\Client\Galmod32 folder on the Exchange 2000 Resource Kit CD-ROM or in the Exchange\operating system\platform\Client\GalMod folder on the Microsoft Back Office Resource Kit, Second Edition CD-ROM.

MORE INFORMATION
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To let users update attributes on their own accounts against the server that is running Microsoft Exchange 5.5 Server (and up...), follow these steps.