Which option are you using to store your data in Microsoft Outlook?

By default, your Outlook data is stored in Personal Folders format (PST) unless you are using an Exchange Server to access your data. If you are using Outlook with an Exchange Server, your data may be stored in an OST file if you have Cached Exchange Mode turned on. An iPhone, iPad, or iPod touch syncing via iTunes will sync with the default PST or OST file. When using an OST file, only information stored locally, or cached on your computer, will be available to sync.

Note: You may be able to sync your iPhone, iPad, or iPod touch directly with your Exchange server. For more information on syncing directly with an Exchange server, contact your Exchange Administrator. There are resources for Exchange Administrators, including the iPhone Enterprise Deployment guide on www.apple.com/support/iphone/enterprise.