Exchange is the server side of a collaborative application product that is part of the Microsoft Server infrastructure. Exchange's major features include email, calendaring, contacts and tasks, support for mobile and web-based access to information, and support for data storage.
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Click Start, click Administrative Tools, and then click Internet Information Services (IIS) Manager.
Double-click to expand the server name, and then double-click to expand the Application Pools folder.
Right-click MSExchangeSyncAppPool, and then click Start to enable Exchange ActiveSync.
After that have a look at this article for step by step procedure http://www.msexchange.org/articles_tutorials/exchange-server-2007/mobility-client-access/mobility-client-access/mobile-messaging-exchange-server-2007-part2.html
"Hope this helps you"