Outlook Mobile Access (OMA) is a great feature in Exchange 2003 that allows cell phone users to access their email from the device. By default OMA is enabled for all users however you may want to restrict this.

There are two ways you can restrict access to OMA, using a script or using a free tool called ADModify. ADModify is a free tool that allows you to mass edit most AD user properties. To modify the OMA settings for your users, open ADModify, select the users you wish to edit and then go to the Exchange Features tab. Here you can edit the OMA settings along with a number of other settings. Uncheck the box to disable the feature or features and click Go to force the change.

ADModify allows you to select specific users to modify but if you want to disable OMA for all users even faster use the following VB script.

You will need to edit cn=Users with the actual OU or OUs that contain the user objects.

For more information see: 

Download ADModify.NET Here

Download VB Script Here